Grade 10 chemisty – Introduction to Chemistry Quiz
1. What is chemistry?
Chemistry is the science that studies matter (what things are made of) and how substances change in reactions; biology studies living things, astronomy studies space, and mathematics studies numbers.
2. Which of the following is an element?
Elements are pure substances made of one type of atom. Oxygen (O2 as a form) is an element; water and sodium chloride are compounds and air is a mixture of gases.
3. Which of the following is a compound?
A compound is a substance made of two or more elements chemically combined; sodium chloride (NaCl) is made of sodium and chlorine atoms joined together. Iron and copper are elements, helium is an element gas.
4. Which subatomic particle has a positive charge and is located in the nucleus?
Protons are positively charged particles in the nucleus. Neutrons have no charge, electrons are negative and located around the nucleus, and photons are particles of light.
5. The atomic number of an element gives the number of:
Atomic number equals the number of protons in an atom's nucleus and determines the element's identity. Electrons equal protons in a neutral atom.
6. The mass number of an atom is the sum of:
Mass number counts the nucleons (protons + neutrons) in the nucleus; electrons have negligible mass compared to nucleons.
7. What is the chemical formula for sodium chloride (table salt)?
Sodium chloride is made of sodium (Na+) and chloride (Cl−) ions in a 1:1 ratio, written NaCl. KCl is potassium chloride, Na2O is sodium oxide, Cl2 is chlorine gas.
8. Which type of chemical bond is formed when two atoms share electrons?
Covalent bonds form when atoms share pairs of electrons (common in molecules like H2O). Ionic bonds form by electron transfer, metallic bonds by a sea of electrons, hydrogen bonds are weak attractions between molecules.
9. An ionic bond usually forms between:
Ionic bonds typically form when a metal donates electrons to a non-metal, producing positive and negative ions that attract each other (e.g., Na and Cl forming NaCl).
10. Which of the following is a physical change?
Melting ice is a physical change where water changes state from solid to liquid without changing chemical identity. Burning, rusting and cooking are chemical changes that form new substances.
11. What does the law of conservation of mass state?
The law states that total mass of reactants equals total mass of products in a chemical reaction (assuming a closed system); mass is conserved.
12. Which of the following is a molecule?
A molecule is two or more atoms chemically bonded; H2O (water) is a molecule composed of hydrogen and oxygen atoms. Na+ and Cl− are ions, Fe refers to single atoms of an element.
13. Which element is an alkali metal found in group 1 of the Periodic Table?
Sodium (Na) is an alkali metal in group 1. Oxygen and chlorine are non-metals; carbon is a non-metal in group 14.
14. Which of the following is a typical property of non-metals?
Non-metals are generally poor conductors of electricity and can be brittle when solid. Metals conduct electricity and are malleable with a metallic luster.
15. A neutral aqueous solution at room temperature has a pH closest to:
pH 7 is neutral (pure water). Lower pH values are acidic and higher values are basic (alkaline).
16. Which laboratory safety practice should you follow when heating chemicals?
Wearing goggles and appropriate protective equipment protects eyes and hands from splashes and burns. Smelling vapours directly and keeping flammables nearby are unsafe.
17. The molar mass (approximate formula mass) of water (H2O) in g/mol is:
Water has two hydrogens (2 × 1 g/mol) and one oxygen (16 g/mol), so its molar mass ≈ 18 g/mol.
18. Which of these is a heterogeneous mixture?
A heterogeneous mixture has visible different components (like soil with stones). Air and true solutions are homogeneous mixtures; sugar solution is homogeneous.
19. What causes iron to rust?
Rust is hydrated iron(III) oxide formed when iron reacts with oxygen and water (oxidation). Dry rubbing or heating without air do not produce rust in the same way.
20. Which property is typical of metals?
Metals conduct electricity and heat well, are often lustrous and malleable. They are not gases at room temperature (except mercury is liquid).
21. Which subatomic particle has the smallest mass?
Electrons have much smaller mass than protons and neutrons. Alpha particles are heavy (two protons and two neutrons).
22. Which unit is used to measure the amount of substance in chemistry?
The mole is the SI unit for amount of substance (6.02 × 10^23 particles ≈ one mole). Kilogram measures mass, liter volume, watt power.
23. Which of the following is a cation?
A cation is a positively charged ion. Na+ is a positive ion (sodium lost an electron). The others are negatively charged anions.
24. Which change will generally increase the rate of a chemical reaction?
A catalyst provides an alternative lower-energy pathway and speeds up reactions without being consumed. Increasing temperature and increasing surface area also speed reactions; decreasing temperature or diluting usually slow them.
25. Which chemical symbol represents the element potassium?
Potassium's chemical symbol is K (from Latin 'kalium'). P is phosphorus, Pt is platinum, Po is polonium.