Toothpaste and its ingredients
After brushing in the morning your mouth feels fresh. In the past people used neem twigs, ash, coal powder or salt; today we use toothpaste.
In toothpaste (टूथपेस्ट) calcium carbonate and calcium hydrogen phosphate scrub the dirt off the teeth and polish them. A small amount of fluoride (फ्लोराइड) protects teeth from decay.
Rule 1: Every ingredient has a fixed job — Some ingredients remove dirt and a different one prevents decay.
- Easy : Calcium carbonate scrubs off the yellowish film on teeth.
- Medium : Fluoride keeps the outer covering of the tooth (enamel) strong, so the risk of decay falls.
- Exam-type : A paste has no fluoride. It will still polish teeth, but protect less against decay.
Fluoride is needed for strong bones and tooth enamel, but toothpaste contains only a small amount.
Thinking tobacco powder (masheri) cleans teeth. It is harmful and must never be used to clean teeth.
Memory clue : "Calcium scrubs, fluoride guards" — calcium scrubs the dirt, fluoride guards the tooth.
Spot the difference
| Ingredient | Job |
|---|---|
| Calcium carbonate | Scrubs dirt, polishes |
| Calcium hydrogen phosphate | Scrubs dirt, polishes |
| Fluoride | Prevents tooth decay |
Practice questions
- 1Which ingredient of toothpaste prevents tooth decay?
- 2Name two things people used in the past for cleaning teeth.
- 3Name two dirt-removing ingredients of toothpaste.
- 4What is the outer covering of a tooth called?
- 5Why do teeth look shiny after brushing with paste?
- 6Why should we read the list of ingredients on a toothpaste pack?
- 7Imagine a paste with only scrubbing ingredients. Which benefit will be missing?
- 8Tanvi says masheri is cheap, so it is good for teeth. What will you tell her?
Show answers (try them yourself first)
- 1Fluoride.
- 2Neem twig and ash (or salt, coal powder).
- 3Calcium carbonate and calcium hydrogen phosphate.
- 4Enamel.
- 5Its ingredients scrub the dirt off and polish the teeth.
- 6To know what we are using and whether it has fluoride.
- 7Protection against tooth decay.
- 8It is harmful and should not be used to clean teeth.
Detergents and surface activity
An oil stain on a shirt does not go with plain water, but it comes out when you rub it with soap.
A substance that wipes or washes away dirt is a detergent (अपमार्जक). Soap nut, soap pod, soap, washing soda, shampoo and washing powder are all detergents.
Rule 1: A detergent joins oil and water — A detergent molecule is long; one end holds water and the other holds oil. So oil mixes with water and the mixture looks milky.
- Easy : Oil and water shaken in a bottle separate again after a while.
- Medium : After adding a few drops of detergent and shaking, the mixture turns milky and uniform.
- Exam-type : Oiled hair rinsed with plain water keeps its oil, because oil does not mix with water. Shampoo molecules hold both oil and water, so the oil washes out.
Rule 2: Surface activity — The property of spreading easily over a surface is surface activity; such a substance is a surfactant (पृष्ठसक्रिय पदार्थ). Lather is one effect of it.
- Easy : Soap water quickly spreads over the cloth.
- Medium : Soap water spreads easily on many surfaces, so it reaches the dirt.
- Exam-type : Saponin in soap nut and soap pod makes the lather. They do not harm skin, so they are considered safe.
Soap nut and soap pod are natural detergents. Their saponin makes lather, and they do not harm skin, silk or wool.
Thinking soap is the only detergent. Soap nut, shampoo and powders are detergents too.
Memory clue : "One end water, other end oil" — the detergent molecule holds both with its two ends.
Spot the difference
| Point | Natural detergent | Man-made detergent |
|---|---|---|
| Example | Soap nut, soap pod | Soap, washing powder |
| Effect on skin | No harm | May irritate in some cases |
Practice questions
- 1What is a detergent?
- 2Name two natural detergents.
- 3Name the chemical in soap nut and soap pod that makes lather.
- 4Why do oil and water separate again after shaking?
- 5Why does the mixture look milky after adding detergent?
- 6What is surface activity?
- 7What do the two ends of a detergent molecule hold?
- 8Why is soap nut considered good for washing a silk saree?
Show answers (try them yourself first)
- 1A substance that wipes or washes away dirt.
- 2Soap nut and soap pod.
- 3Saponin.
- 4They do not mix with each other.
- 5Tiny oil droplets spread through the water.
- 6The property of spreading easily on a surface.
- 7One end water, the other end oil.
- 8It does not harm silk.
Soap: types and hard water
A bathing soap feels soft while a washing bar is hard. In some well water, though, soap gives no lather.
Soap (साबण) is a sodium or potassium salt of fatty acids. It forms when fat or oil reacts with an alkali.
Rule 1: Two kinds of soap — Sodium soap is hard and used for clothes. Potassium soap is soft, used for bathing, and does not irritate skin.
- Easy : The hard washing bar is a sodium salt.
- Medium : The soft bathing soap is a potassium salt.
- Exam-type : If a soap irritates your skin, a soft potassium soap is the right choice for bathing because it does not irritate skin.
Rule 2: Soap fails in hard water — In hard water soap gives no lather and forms a sticky scum, so it loses its cleaning power. Synthetic detergents work even in hard water.
- Easy : Soap lathers in soft tap water but not in hard well water.
- Medium : After washing in hard water, a whitish film and spots may remain on clothes.
- Exam-type : Borewell water that is hard defeats soap; a synthetic detergent should be used there because it forms no scum.
While making soap, salt solution is added at the end; the soap then floats up and thickens.
Thinking soap lathers in hard water but cannot clean. In fact it does not lather and forms scum.
Memory clue : "Hard = Sodium = Clothes; Soft = Potassium = Bath" — remember the type and its use together.
Spot the difference
| Point | Hard soap | Soft soap |
|---|---|---|
| Salt | Sodium | Potassium |
| Use | Washing clothes | Bathing |
| On skin | Rough | Does not irritate |
Practice questions
- 1What is soap?
- 2Washing soap is a salt of which metal?
- 3Which kind is a bathing soap?
- 4Soap is formed by the reaction of what?
- 5What happens to soap in hard water?
- 6Why is salt added at the end of soap making?
- 7Which detergent works in hard water, and why is soap not suitable?
- 8How will you test with soap whether water is hard?
Show answers (try them yourself first)
- 1A sodium or potassium salt of fatty acids.
- 2Sodium.
- 3Soft, a potassium salt.
- 4Fat or oil and an alkali.
- 5It does not lather and forms scum.
- 6So that the soap floats up and thickens.
- 7Synthetic detergent works; soap forms scum.
- 8Shake soap in a little water; if scum forms instead of lather, the water is hard.
Cement and concrete
Cement is used in building houses, bridges, roads and water tanks to keep them strong.
Cement (सिमेंट) is a dry, greenish-grey fine powder made from silica (sand), alumina, lime, iron oxide and magnesia. Mixing cement, water, sand and gravel gives concrete (काँक्रीट).
Rule 1: Portland cement — Portland cement is the most used cement in construction. Its raw material has about 60% lime, 25% silica and 5% alumina; the rest is iron oxide and gypsum.
- Easy : The biggest ingredient of Portland cement is lime.
- Medium : It got its name from a stone of the Isle of Portland in England that it resembles.
- Exam-type : In 100 kg of raw material with 60% lime, the lime is 60 kg.
Rule 2: Concrete and the history of cement — Concrete is used for sheets, blocks, pillars, pipes and roads. The Romans mixed volcanic ash with moist lime to make durable cement; in 1756 the British engineer John Smeaton developed a method of making cement that sets under water.
- Easy : Pillars and pipes are made from concrete.
- Medium : Besides cement, concrete contains water, sand and gravel.
- Exam-type : Without cement the sand and gravel do not bind, so the slab crumbles.
Cement is the "glue" of construction. It binds sand and gravel firmly together.
Cement and concrete are not the same. Cement is a powder; concrete is a mixture of cement, water, sand and gravel.
Memory clue : "Cement = glue, concrete = the firm mix" — glue + sand + gravel + water = concrete.
Spot the difference
| Point | Cement | Concrete |
|---|---|---|
| Form | Dry fine powder | Setting mixture |
| Made of | Lime, silica, alumina etc. | Cement, water, sand, gravel |
Practice questions
- 1How does cement look?
- 2What is concrete made from?
- 3Which cement is used the most?
- 4Which is the largest ingredient of Portland cement?
- 5Name two things made from concrete.
- 6How did the Romans make durable cement?
- 7In 50 kg of raw material with 25% silica, how much silica is there?
- 8What problem arises if a road is made only of sand and gravel?
Show answers (try them yourself first)
- 1A greenish-grey dry fine powder.
- 2Cement, water, sand and gravel.
- 3Portland cement.
- 4Lime (about 60%).
- 5Pillars and pipes (or sheets, blocks).
- 6By mixing volcanic ash with moist lime.
- 712.5 kg.
- 8They will not bind together; the road will crumble.