NAFES Practice

Front

Which is the best example of a new substance forming? Options: lighting a match, cutting a piece of paper, popping a balloon, hitting a nail with a hammer

Back

lighting a match

Answer explanation

The best example of a new substance forming is lighting a match, as it involves a chemical reaction that creates a new substance (fire) from the matchstick and oxygen.

Front

What caused the change of a piece of iron from shiny to rusty?

Back

a chemical reaction

Answer explanation

Students observed a piece of iron change from shiny to rusty due to a chemical reaction, not a heat or cold reaction. The rusting process involves a chemical reaction with oxygen in the air.

Front

Which of the following is a chemical property of water?

• Reacts with pure sodium
• Boils at 100 ^oC
• Is liquid at room temperature
• Has a density of 1 gm/mL

Back

Reacts with pure sodium

Answer explanation

The correct choice is 'Reacts with pure sodium' because this is a chemical property of water, indicating its ability to undergo a chemical reaction with sodium.

Front

Which of the following is an example of sublimation? Dry Ice, Water boiling into steam, Ice cream melting, Water freezing into ice

Back

Dry Ice

Answer explanation

Dry Ice is an example of sublimation because it changes directly from a solid to a gas without passing through the liquid phase.

Front

Which phrase most accurately describes a chemical change?

Back

A change on the molecular level.

Answer explanation

The phrase 'A change on the molecular level' most accurately describes a chemical change as it involves alterations at the molecular level, distinguishing it from changes in appearance, taste, or size.

Front

Which of the following is NOT an example of a physical change?

• crumpling paper
• sharpening a pencil
• clothes shrinking
• sour milk

Back

sour milk

Answer explanation

The correct choice is 'sour milk' because it involves a chemical change, not a physical change like the other options.

Front

What pH is the strongest base?

Back

14

Answer explanation

The strongest base has a pH of 14, as it is the highest value on the pH scale indicating a high concentration of hydroxide ions.

Front

Milk is a very weak acid. What might its pH value be?

Back

6.5

Answer explanation

Milk, being a weak acid, would have a pH value around 6.5, making the correct answer choice 6.5.

Front

Which of the following statements is correct?

• Blue litmus paper turns red when placed in a base.
• Red litmus paper turns blue when placed in a base.
• Blue litmus paper stays blue when placed in an acid.
• Red litmus paper stays red when placed in a base.

Back

Red litmus paper turns blue when placed in a base.

Answer explanation

Red litmus paper turns blue when placed in a base.

Front

Unit for mass of an object

Back

gram

Answer explanation

The correct unit for mass of an object is 'gram'. It is a metric unit used to measure the mass of small objects.