Elements and compounds
Grade 8 Science Worksheet - Building Confidence
Circle the best answer, or write your answer on the line.
A box holds 2 molecules of C₂H₆O. How many atoms are in the box altogether, Ari?
Bo's sheet shows 2 molecules of H₂SO₄. How many atoms is that altogether?
Baking soda is NaHCO₃. A tray holds 3 units of it. How many atoms is that in all, Esme?
Jun says this box holds a compound because the atoms are joined. Is that right?
- Yes: each particle has two atoms in it, and two atoms make a compound
- No: every ball is one kind, so it is an element
- Yes: joined atoms always make a compound, whatever kind they are
- No: it is a mixture, since the balls are separate from each other
All the particles in this box match. Kira says it must be an element. Is that right?
- No: each particle holds H and O joined, so a compound
- No: it is a mixture of H and O gases stirred together
- Yes: water is very common, so it must be an element
- Yes: identical particles mean they hold a single kind of atom
What kind of matter is in this box, Luz?
- A compound, since it has two kinds of atoms in it
- A mixture of elements: He and N₂ are not joined
- A compound, since it has a joined pair of atoms
- A compound of He and N, since both are in one box
Milo's sulfur sample has the formula S₈. Is it an element or a compound, and why?
- An element, since all eight atoms are sulfur
- A compound, since the eight atoms are joined together
- A compound, since eight atoms mean eight different kinds
- A mixture, since the eight atoms are mixed together
Baking soda is NaHCO₃. How many kinds of atoms does it have, and what is it, Noah?
- Three kinds: Na, H and CO, so it is a compound
- Six kinds, since it has six atoms in total
- Four kinds (Na, H, C, O): a compound
- Two kinds: Na and HCO₃, so it is a compound
Read this first
Baking soda and vinegar (example data)
observation before mixing after mixing what is in the cup white powder and clear liquid bubbling liquid temperature (°C) 22 17 Baking soda meets vinegar in a cup. Which clue best shows a new substance formed, Ren?
- The powder was gone, so it must have melted
- Gas bubbles formed that were not there before
- The temperature changed, and any change means a new substance
- Nothing new formed, since the same atoms are in the cup
Ice melts, wood burns and sugar dissolves in tea. Which one is a chemical change, and why, Tala?
- Wood burning, since ash and gas are new substances
- The three together, since each change makes new substances
- Sugar dissolving, since the sugar seemed to disappear
- Ice melting, since it changed from a solid to a liquid