Checkpoint: new substances and the two questions

Air is blown into lime water. It turns milky. What does this show?

• The lime water has only changed its shape
• Lime water always turns milky when it is stirred
• The air has carbon dioxide, which makes a new white solid

A hot pan of water gives off steam. A gas comes off. Which is true?

• Water cannot give off a gas
• A gas came off, so a new substance is made
• Steam is water, so no new substance is made

A candle burns for a while. Which step is a chemical change?

• The melted wax climbs the wick
• The wax melts near the wick
• The wax vapour burns at the flame

Which change makes no new substance, and also cannot be undone?

• Milk turning to curd
• Ice melting in a glass
• A chalk stick ground to powder

Water freezes in a crack and splits a rock. What kind of change is this?

• Physical. The rock is broken, but it is still rock
• Chemical, because water is new
• Chemical, because it took a long time