Chemicals Used in Daily Life

Detergent is more polluting than soap because:

1. Non-biodegradable: Many detergents (with branched-chain hydrocarbon groups) cannot be broken down by bacteria, so they accumulate in soil and water. Soap is made from natural fats/oils and is biodegradable.
2. Phosphates and other chemicals: Detergents contain phosphates, bleaches and synthetic chemicals. These cause eutrophication (excess algae growth), reduce dissolved oxygen and harm fish and other aquatic life.
3. Foam: Persistent foam on rivers and lakes blocks sunlight and oxygen.

(b) detergent

A detergent cleans like soap but is not a fatty-acid salt, so it is chemically different from soap. That is why it is called a soapless soap.

(d) Statement and argument 1 are correct but argument 2 is wrong.

Soap is made from natural fats and is biodegradable, so it is environment friendly (statement and argument 1 correct). Scum formation in hard water is a drawback of soap, not a reason for being eco-friendly, and it makes cleaning less effective, so argument 2 is wrong.

Food preservatives are used to prevent the growth of microorganisms (bacteria, fungi, yeast) and oxidation, so that food does not spoil and can be stored for a long time.

(c) Calcium carbide

Calcium carbide reacts with moisture to give acetylene gas, which acts like the natural ripening hormone ethylene and ripens fruits quickly. (Its use is banned because it harms health.)

Precautions while using pesticides:

1. Wear protective clothing (mask, gloves, boots, full-sleeved clothes) while spraying and wash hands and body after use.
2. Spray in the direction of wind, not in strong wind or rain, and use only the recommended dose.
3. Do not eat, drink or smoke while spraying; keep pesticides away from children, food and water sources, and stop spraying some days before harvest.

Chemical pesticides are dangerous to human health because:

1. Residues in food: Pesticides remain on vegetables, fruits and grains and enter the body through food and water, causing poisoning, vomiting, headache, and over a long time cancer, liver and kidney damage and nervous system disorders.
2. Accumulation (biomagnification): Persistent pesticides like DDT are not easily broken down; they build up in the food chain and in body fat, harming health, and farmers who spray them without protection may suffer skin and breathing problems.

(a) Statement and argument 1 are correct but argument 2 is incorrect.

Detergent is called a soapless soap because it cleans like soap but is not a fatty-acid salt, so its chemical nature is different. This is exactly what argument 1 says, so the statement and argument 1 are correct.

Argument 2 (soap causes no chemical pollution, detergent does) is too absolute and does not explain the name. Soap is biodegradable and pollutes much less, but it is not entirely free of pollution. Of the options, only (a) marks the statement and argument 1 as correct.

(d) Exhibits cleansing properties like soap but chemically different from soap.

Detergents are not fatty-acid salts, so they are chemically different, yet they clean like soap.

(a) Detergents work well in both hard and soft water, whereas soap is less effective in hard water.

Soap forms scum with calcium and magnesium ions of hard water, but detergent forms soluble salts and so lathers and cleans well. Soap is the more biodegradable and less polluting of the two, so (b) and (d) are wrong.

Detergent is more efficient because it does not form scum with hard water (its calcium and magnesium salts are soluble), so it lathers and removes dirt well even in hard water and cold water. It also contains additives (bleach, brighteners, enzymes) that give better cleaning.

• Person A (hot water with soap): Hot water dissolves soap better and loosens grease and dirt; it also helps to reduce temporary hardness of the water by boiling (removing bicarbonates of Ca/Mg), so less scum forms.
• Person B (detergent): Detergent does not form scum with the hardness salts of tap water, so it lathers and cleans well even in cold, hard water.

Saponin. Reetha (soapnut) contains saponin, which produces foam in water and acts as a natural cleansing agent.

Reetha (soapnut) or shikakai. They contain saponin, a natural foaming and cleaning agent that is biodegradable and does not pollute the environment.

Ammonium hydroxide ($NH_4OH$).

$NH_3 + H_2O \rightleftharpoons NH_4OH$

Urea is made from ammonia and carbon dioxide at high temperature and pressure:

$2NH_3 + CO_2 \xrightarrow{\text{high temp., pressure}} NH_2CONH_2 + H_2O$

X = $\mathrm{Na_2O}$ (sodium oxide).

It is a neutralisation reaction between a basic oxide and an acid giving salt and water. ($\mathrm{NaOH}$ would require the balanced equation $2\mathrm{NaOH} + \mathrm{H_2SO_4} \rightarrow \mathrm{Na_2SO_4} + 2\mathrm{H_2O}$, so it does not match the given equation as written.)

During long fasting, the stomach has no food, but it keeps producing hydrochloric acid, causing acidity and stomachache.

I would suggest an antacid such as milk of magnesia, magnesium hydroxide $Mg(OH)_2$. It neutralises the excess acid:

$Mg(OH)_2 + 2HCl \rightarrow MgCl_2 + 2H_2O$

(Sodium bicarbonate also works: $NaHCO_3 + HCl \rightarrow NaCl + H_2O + CO_2$.)

Industrial chemical waste is managed by:

1. Treating the waste (neutralisation, filtering, chemical or biological treatment in an effluent treatment plant) before discharging it into rivers or soil.
2. Reducing, reusing and recycling chemicals and by-products, and safely storing or burying hazardous waste in proper landfills.
3. (Also) following laws and standards, and using eco-friendly raw materials and technology.

Soil erosion and loss of fertility from excess chemical fertilizers can be controlled by:

1. Reducing chemical fertilizers and using organic manure, compost and green manure, which improve soil structure and bind soil.
2. Applying the correct dose of fertilizer at the right time, practising crop rotation and terracing/contour ploughing, and planting grass or trees to hold the soil.

Definition: A food preservative is a natural or chemical substance added to food to prevent its spoilage by microorganisms or oxidation and to keep it fresh for a long time.

Example: Common salt, sugar, vinegar, sodium benzoate.

Points to remember while using:

1. Use only permitted preservatives in the recommended (small) amount, since excess is harmful to health.
2. Mix it properly and store the food in clean, air-tight containers; do not use preservatives to hide stale or already spoilt food.

Advantages of food preservatives:

1. They keep food fresh and safe for a long time by preventing the growth of microorganisms, so food is not wasted.
2. Food can be stored, transported to distant places and available in off-season.

Natural food preservatives (salt, sugar, vinegar, oil, spices) are better.

They are safe, cheap, locally available and have no harmful side effects, whereas chemical preservatives like sodium benzoate may cause allergy, headache, or long-term health problems if used in excess.

(d) Mixing with oil

Oil is a natural preservative (used in pickles); it forms a layer which keeps air out and stops microorganisms. Sodium benzoate, potassium sorbate and benzoic acid are chemical preservatives.

Natural ways to preserve potato:

1. Store in a cool, dry, dark and well-ventilated place (e.g. in sand, straw or baskets), since light causes greening and sprouting.
2. Keep dry and remove damaged or rotten ones; storing with dry leaves of some herbs or ash can also reduce sprouting. Potato can also be sun-dried as chips.

The pickle spoiled because the open jar let in air, moisture and microorganisms (fungi and bacteria), which grew on it, and the preservative effect of oil/salt/vinegar was lost.

To prevent this: keep the jar tightly closed after use, use a dry clean spoon, keep it covered with oil, add enough salt, vinegar and spices, and store in a cool, dry place.

Method: Mixing the pickle with salt, mustard oil, vinegar and spices (like turmeric, chilli) and keeping it in an air-tight jar. Salt removes water from microbes, oil seals out air and acidity of vinegar stops microbial growth.

Advantage: It is natural, cheap, easily available and harmless to health (keeps the food safe for months without refrigeration).

Chemical used: Calcium carbide ($CaC_2$), which gives acetylene gas (with traces of arsenic and phosphorus impurities) on contact with moisture.

Other chronic effect: Excessive use may cause cancer, damage to the nervous system (memory loss, neurological damage), and liver and kidney damage, and also headache, dizziness and stomach ulcers.

Home methods to ripen bananas:

1. Cover the bunch with straw, paddy husk or banana/neem leaves (or wrap in a cloth/newspaper) and keep it in a closed warm room or basket for 2-3 days. The ethylene gas released by the fruits themselves ripens them.
2. Keep the bananas in a paper bag or pit together with a ripe banana or ripe mango/apple, which release extra ethylene, and tie the opening.

1. Traditional methods use natural ethylene and straw, leaves, etc., so the fruits are safe; chemicals like calcium carbide leave toxic residues causing cancer, neurological and skin problems.
2. Traditional ripening is cheap, simple and easily available and keeps the natural taste, colour and nutrients of fruits, and it is also eco-friendly and legal, whereas carbide is banned by the Food Act.

The cheap, easily found chemical used to ripen mango and banana is calcium carbide. Strictly it is a ripening agent, not a true preservative.

Adverse effect: Excessive use may cause cancer, damage to the nervous system (neurological damage), headache, dizziness and weakness, and skin and eye irritation. Residues of arsenic and phosphorus from it are poisonous.

1. Use pesticides in the recommended amount only, with protective clothing, and wash fruits and vegetables well (and wait for the safe period before harvest) before eating.
2. Reduce chemical use by adopting organic farming and biological/integrated pest management (neem extract, bio-pesticides, natural predators, crop rotation), and use biodegradable, non-persistent pesticides instead of DDT-like ones.

Insecticide kills insects that damage crops (e.g. DDT, malathion), whereas herbicide kills unwanted weeds growing with crops (e.g. 2,4-D, butachlor).

(a) Herbicide: Butachlor (also 2,4-D, glyphosate), which kills weeds.

(b) Fungicide: Carbendazim (also Bordeaux mixture, copper sulphate, mancozeb), which kills fungi.

(b) Carbendazim

Carbendazim is used to control fungal diseases. Cypermethrin is an insecticide, butachlor a herbicide and zinc phosphide a rodenticide.

(d) Bromadiolan, cumatetralyl, zinc phosphide.

All three are used to kill rats and other rodents. Malathion, aldrin, BHC and DDT are insecticides.

(i) DDT, BHC, aldrin

All three are chemical insecticides (organochlorines). The other groups contain items like potassium chloride, benzene and benzoic acid, which are not insecticides.

(i) Statement and argument 1 are correct but argument 2 is incorrect.

Persistent insecticides (e.g. DDT) do not degrade quickly in the environment, so they collect and accumulate in soil, water and living things (argument 1 correct). Argument 2 describes a non-persistent insecticide, so it is incorrect.

The raw materials of cement are limestone (calcium carbonate) and clay (or shale), with a little gypsum added at the end to control setting.

The fertilizer formed is urea, $CO(NH_2)_2$:

$CO_2 + 2NH_3 \to CO(NH_2)_2 + H_2O$

The base that contains no metal is ammonium hydroxide, $NH_4OH$.

$HNO_3$ (nitric acid) is the acid. NaCl and $Na_2CO_3$ are salts, and CaO is a basic oxide.

The plastic that is affected (softened) by heat is called thermoplastic, e.g. PVC and polythene. In contrast, a thermosetting plastic is a plastic that is hardened once by heating and moulding, and cannot be softened or remoulded on reheating, e.g. bakelite and melamine.

Cement clinker is the hard, greyish lumps (balls) formed when a mixture of limestone and clay is strongly heated in a rotary kiln at about 1400-1500 °C. It is ground with a little gypsum to make cement.

$CH_3COOH$ (acetic acid) is the organic acid. HCl, $H_2SO_4$ and $HNO_3$ are mineral (inorganic) acids.

Two applications of neutralization in daily life:

1. Antacid tablets (e.g. milk of magnesia, $Mg(OH)_2$) neutralize excess acid in the stomach and relieve indigestion.
2. Lime ($CaO$ or $Ca(OH)_2$) is added to acidic soil to neutralize it and make it fit for crops. (Baking soda or ammonia applied to a bee/ant sting also neutralizes the acid.)

(a) PVC is a thermoplastic. It softens and melts on heating, so it would melt and deform from the heat of the cooker. A heat-resistant thermosetting plastic such as bakelite is used instead.

(b) Melamine is a thermosetting plastic. Its molecules form strong cross-links when it is heated and set for the first time, so it cannot be softened and remoulded again by heating.

(a) The pressure cooker handle is made of bakelite, whose raw materials are phenol and formaldehyde.

(b) Lens glass (optical glass) is made from silica sand ($SiO_2$) with lead oxide and potassium carbonate (potash) (flint glass), or with soda ash and limestone for ordinary glass.

$H_2SO_4$ is a strong acid that ionizes completely to give many $H^+$ ions, so it reacts readily with zinc to release hydrogen steadily. $H_2CO_3$ is a weak, unstable acid; it ionizes only slightly and decomposes into $CO_2$ and water, so the gas would be impure and the reaction very slow.

$Zn + H_2SO_4 \to ZnSO_4 + H_2\uparrow$

OR

Two reasons: (i) $H_2SO_4$ is a strong acid, but $H_2CO_3$ is weak and gives few $H^+$ ions; (ii) $H_2CO_3$ is unstable and breaks down into $CO_2$ and $H_2O$, so the hydrogen would be contaminated.

(a) X is hydrochloric acid, HCl, as $HCl \to H^+ + Cl^-$.

(b) $Mg(OH)_2$ (milk of magnesia) would be suggested. It is a weak base and is not harmful, while NaOH is a strong corrosive base and $Na_2CO_3$ is too strongly basic and releases $CO_2$.

(c) The hydrogen ion ($H^+$, proton) is responsible for turning methyl orange red.

(a) To pack an electronic device: Polystyrene (thermocol), as it is light and shock-absorbing.

(b) To cover the antenna of a spacecraft: Quartz (fused quartz), as it is heat-resistant and lets radio waves pass through.

(c) To make a non-sticky surface of cooking vessels: Teflon.

(a) Waste glass is non-biodegradable, so it causes land pollution (broken pieces also injure people and animals).

(b) Used glass can be collected, recycled and reused (also reuse bottles instead of throwing them).

(c) Polycarbonate glass is used in making sunglasses and spectacles to protect the eyes from harmful UV rays.

(a) PVC is better for recycling, as it is a thermoplastic that can be melted and remoulded.

(b) Bakelite is better for an electrical insulation board, as it is a thermosetting plastic and a poor conductor of heat and electricity.

(c) Bakelite remains hard in hot water, as it does not soften on heating, while PVC would soften.

(a) The indicator is methyl orange: it is orange in neutral solution, yellow in base and red in acid.

(b) Beaker A (orange) contains a neutral solution.

(c) Beaker B is basic (yellow) and C is acidic (red). Mixing them gives a neutralization reaction, for example:

$NaOH + HCl \to NaCl + H_2O$

OR

The reaction between B and C is a neutralization reaction (a double displacement reaction).

(a) For example:

$HCl + NaOH \to NaCl + H_2O$

(b) C is NaCl, which ionizes as

$NaCl \to Na^+ + Cl^-$

$Na^+$ is the basic radical because it comes from the base NaOH, and $Cl^-$ is the acidic radical because it comes from the acid HCl.

OR

(a) It is called neutralization because the acid and the base react with each other and cancel their properties, forming a neutral salt and water.

(b) As above, $NaCl \to Na^+ + Cl^-$. $Na^+$ is the basic radical (from NaOH) and $Cl^-$ is the acidic radical (from HCl).

(a) $Mg(OH)_2$ is suitable. It is a weak base, so it neutralizes the excess acid safely without harming the stomach. $Ca(OH)_2$ is a strong, corrosive base, and $Na_2CO_3$ is strongly basic and gives off $CO_2$, which causes gas and discomfort.

(b) The excess hydrochloric acid is neutralized:

$Mg(OH)_2 + 2HCl \to MgCl_2 + 2H_2O$

OR

The antacid (base), e.g. milk of magnesia, reacts with the excess HCl in the stomach to form a neutral salt and water, which reduces the acidity.

(a) The compound is nitric acid, $HNO_3$.

(b) Blue litmus paper turns red.

(c) Dilute nitric acid reacts with calcium oxide (a base) to form calcium nitrate and water:

$2HNO_3 + CaO \to Ca(NO_3)_2 + H_2O$

(c) Statement and argument 1 are correct but argument 2 is incorrect.

Detergent is called soapless soap because it cleans like soap but is chemically different (argument 1 is correct). However, detergent does give lather in hard water because its calcium and magnesium salts are soluble. So argument 2 is wrong.

Salt or sugar makes a concentrated solution around the food. By osmosis, water leaves the bacterial cells and the cells shrink (plasmolysis). Without water, bacteria cannot grow or multiply, so the food is not spoiled.

i. Other effects of calcium carbide on health: headache, dizziness, vomiting, skin rashes, burning of eyes and throat, ulcers in the stomach, and long-term cancer or kidney and liver damage.

ii. Traditional ripening: Place the unripe fruits (mango, banana) in a closed basket or jar/pit with straw, paddy husk or leaves, or wrap them in newspaper/cloth and keep in a warm place for a few days. Fruits release natural ethylene gas, which ripens them. Keeping them with already ripe fruit speeds the process.

(c) Statement and argument 1 are correct but argument 2 is incorrect.

A stomach pesticide is applied on leaves and fruits and kills insects when they eat the treated plant (argument 1 correct). Releasing poisonous gas on contact with air is the mode of a fumigant, so argument 2 is incorrect.