Nature of Matter: Elements, Compounds, and Mixtures

An ELEMENT is BEST defined as a substance:

1. aThat always exists as a gas
2. bThat cannot be broken down into simpler substances by ordinary chemical means
3. cThat is a mixture of metals
4. dThat always conducts electricity

Which of the following is an element?

1. aWater
2. bBrass
3. cSulphur
4. dSalt

Which of the following is a COMPOUND?

1. aIron filings
2. bBrass
3. cAir
4. dSodium chloride (common salt)

Which of the following is a UNIFORM mixture?

1. aSand and iron filings
2. bOil and water
3. cSalt dissolved in water
4. dGranite stone

Air is BEST classified as:

1. aA pure substance
2. bA uniform mixture of several gases (mostly \(\ce{N2}\) and \(\ce{O2}\))
3. cA compound with formula \(\ce{NO2}\)
4. dAn element

Which one of the following statements is TRUE for a MIXTURE?

1. aComponents are present in a fixed ratio
2. bComponents retain their original properties
3. cIt is always a new substance
4. dIt can never be separated

1. I. Pure water is an example of a compound.
2. II. A solution of sugar in water is a non-uniform mixture.
3. III. Air is a mixture of several gases.

Which of the above statements about pure substances and mixtures are correct?

1. aI and II only
2. bI, II and III
3. cII and III only
4. dI and III only

Assertion (A): All atoms of a given element are alike in their basic chemical behaviour.

Reason (R): An element is a pure substance made up of only one kind of atom.

1. aBoth A and R are true, and R is the correct explanation for A
2. bBoth A and R are true, but R is NOT the correct explanation for A
3. cA is true, but R is false
4. dA is false, but R is true

When dry sugar is heated gently in a boiling tube, it turns brown, then black, and water droplets collect near the mouth of the tube. What can be concluded about sugar?

1. aSugar is an element, because heating it leaves a black solid behind
2. bSugar is a mixture, because its colour changes on heating
3. cSugar is a compound of carbon, hydrogen and oxygen, because it breaks down into simpler substances
4. dNothing can be concluded, because the water droplets came from the air

When iron and sulphur are HEATED till they glow and form iron sulphide, the new substance is:

1. aA simple mixture from which iron can still be separated by a magnet
2. bPure iron
3. cA new compound (\(\ce{FeS}\)) — black, with properties different from those of iron and sulphur
4. dPure sulphur

Match each substance with its CORRECT classification:

1. a(i)-P, (ii)-R, (iii)-Q, (iv)-S
2. b(i)-Q, (ii)-R, (iii)-P, (iv)-S
3. c(i)-P, (ii)-S, (iii)-Q, (iv)-R
4. d(i)-S, (ii)-P, (iii)-Q, (iv)-R

Which of the following is the BEST evidence that pure water is a compound, not a mixture, of hydrogen and oxygen?

1. aWater tastes neutral
2. bOn electrolysis water decomposes into hydrogen and oxygen in a fixed ratio of 2 : 1 by volume
3. cWater freezes at 0 °C
4. dWater can dissolve salt

1. I. A compound has properties that are different from those of the elements it is made of.
2. II. Components of a compound can be separated by physical methods such as filtration.
3. III. Iron sulphide (\(\ce{FeS}\)) is a compound.

Which of the above statements about compounds are correct?

1. aI and II only
2. bI, II and III
3. cII and III only
4. dI and III only

Assertion (A): Common salt (\(\ce{NaCl}\)) is a compound and not a mixture of sodium and chlorine.

Reason (R): A compound is formed when different elements combine chemically in a fixed ratio, and its properties are different from those of its elements.

1. aBoth A and R are true, and R is the correct explanation for A
2. bBoth A and R are true, but R is NOT the correct explanation for A
3. cA is true, but R is false
4. dA is false, but R is true

Which of the following techniques is BEST for separating salt from sea water on a small scale?

1. aFiltration through ordinary filter paper
2. bMagnetic separation
3. cEvaporation of the water until salt crystals are left behind
4. dDecantation

When electricity is passed through water (with a few drops of acid added), gases collect in two test tubes. A burning candle brought near one test tube gives a ‘pop’ sound; near the other, the flame glows brighter. The gases are:

1. aPop sound: hydrogen; brighter flame: oxygen
2. bPop sound: carbon dioxide; brighter flame: nitrogen
3. cBoth test tubes contain water vapour
4. dPop sound: oxygen; brighter flame: hydrogen

Which of the following elements is a metal that is a liquid at room temperature?

1. aBromine
2. bGallium
3. cSodium
4. dMercury

Silicon and boron are called metalloids because they:

1. aAre compounds of a metal and a non-metal
2. bHave properties in between those of metals and non-metals
3. cAre liquids at room temperature
4. dAre mixtures of two metals

Which of the following statements about minerals is correct?

1. aAll minerals are pure elements
2. bMinerals are mixtures with no fixed composition
3. cMinerals are always metals
4. dMost minerals are compounds, but some, such as gold and copper, are pure elements

Assertion (A): Salt and water can be separated easily by physical means.

Reason (R): A mixture can be separated into its components by physical methods because its components retain their original properties.

1. aBoth A and R are true, and R is the correct explanation for A
2. bBoth A and R are true, but R is NOT the correct explanation for A
3. cA is true, but R is false
4. dA is false, but R is true

Which of the following is the BEST description of an ALLOY?

1. aA naturally occurring pure metal
2. bA uniform mixture of two or more metals (sometimes with a non-metal such as carbon)
3. cA compound formed by two metals
4. dA pure non-metal

1. I. Soda water is a mixture of a gas and a liquid.
2. II. Carbon particles in air form a mixture of a liquid and a gas.
3. III. Baking powder (baking soda and tartaric acid) is a mixture of two solids.

Which of the statements above about types of mixtures is/are correct?

1. aOnly I and II
2. bOnly II and III
3. cOnly I and III
4. dI, II and III

The word ‘pure’ on a packet of spices usually means that nothing cheaper or of poor quality has been added. In science, a pure substance is:

1. aA substance that has no other substance in it and is made of the same type of particles
2. bA product made only from natural ingredients
3. cAny packed product that has no adulterant added to it
4. dA mixture whose components are evenly spread throughout

Riya pours clear, filtered lime water into a petri dish and leaves it on her classroom table for a few hours, stirring it now and then. It slowly turns milky. Which statement correctly explains her observation?

1. aCarbon dioxide in the air reacts with calcium hydroxide to form insoluble calcium carbonate
2. bOxygen in the air reacts with calcium hydroxide to form calcium oxide
3. cWater vapour in the air dilutes the lime water and makes it cloudy
4. dNitrogen in the air reacts with calcium hydroxide to form calcium carbonate

Assertion (A): Light and heat are forms of matter.

Reason (R): Matter is anything that has mass and takes up space.

1. aBoth A and R are true, and R is the correct explanation for A
2. bBoth A and R are true, but R is NOT the correct explanation for A
3. cA is true, but R is false
4. dA is false, but R is true

Which of the following is the BEST example of a CHEMICAL change?

1. aCrushing chalk into powder
2. bMixing salt and pepper
3. cBurning a piece of paper
4. dCutting a wire into pieces

When a magnet is held above bottle 3 (mixed iron + sulphur), what is observed?

1. aBoth iron and sulphur jump up to the magnet
2. bNothing is attracted
3. cOnly sulphur is attracted
4. dOnly iron filings are attracted to the magnet

When a magnet is held above bottle 4 (iron sulphide formed by heating), what is observed?

1. aIron is still attracted, just like before
2. bNothing is attracted because iron is now chemically locked into the compound \(\ce{FeS}\)
3. cThe bottle gets warm
4. dSulphur catches fire

When dilute \(\ce{HCl}\) is added to bottle 3 vs bottle 4, which gas is given off in EACH case?

1. aBoth give hydrogen only
2. bBoth give carbon dioxide
3. cBoth give \(\ce{H2S}\)
4. dBottle 3 gives hydrogen (\(\ce{H2}\)) from iron + \(\ce{HCl}\); bottle 4 gives hydrogen sulphide (\(\ce{H2S}\)) from \(\ce{FeS + HCl}\)

From the four bottles together, the BEST single conclusion the visitors can draw is that:

1. aA compound and its parent elements have the same properties
2. bIron and sulphur cannot react with each other
3. cA mixture keeps the properties of its components, but a compound has new properties of its own
4. dAll bottles contain the same substance