Chemical reactions: signs of a new substance, and counting atoms
Grade 8 Science Worksheet
Circle the best answer, or write your answer on the line.
In 4 Fe + 3 O₂ → 2 Fe₂O₃, how many oxygen atoms are in 2 Fe₂O₃, Ari?
In 6 CO₂ + 6 H₂O → C₆H₁₂O₆ + 6 O₂, how many oxygen atoms are in 6 O₂, Bo?
In 6 CO₂ + 6 H₂O → C₆H₁₂O₆ + 6 O₂, how many hydrogen atoms are in 6 H₂O, Esme?
Read this first
Equation
2 Cu + O₂ → 2 CuO. An atom-count table sits under it with one row per element and columns for left and right, left blank.
Jun checks an equation for copper joining with oxygen. Is it balanced?
- No: oxygen disappears
- No: 3 molecules on the left, 2 on the right
- Yes: 2 Cu and 2 O on each side
- No: copper is not on the right
A teacher boils water, and bubbles rise. Is this a chemical reaction, Milo?
- No: the bubbles are water as a gas
- Yes: bubbles mean a reaction
- Yes: a gas formed
- Yes: the water became a new substance
Noah adds a drop of food coloring to water, and the color spreads. Is this a reaction?
- Yes: a color change is a reaction
- Yes: new dye atoms formed
- Yes: the water became a new liquid
- No: the dye only mixed in
A teacher lights a candle while the class watches. Which part is a chemical change, Pia?
- Wax burning into carbon dioxide and water
- Wax melting near the wick
- Wax atoms vanishing as it burns
- Melted wax hardening again
Ren mixes baking soda and vinegar in an open cup on a scale. The reading drops by about 2 g. Why?
- The scale got wet
- The gas weighs less than nothing
- Some atoms were destroyed
- Gas escaped into the air
Tala repeats the test in a sealed zip bag. What does the scale show after the fizzing?
- Less, since gas has no mass
- Twice as much
- The same mass
- Less, since atoms were used up
Damp steel wool on a scale weighs a little more after it rusts for a week. Why, Zee?
- Oxygen from the air joined the iron
- Oxygen has no mass, so it must be dust
- New iron atoms were made
- Iron gets heavier when cold