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Chemistry 1
Core Science Model Answers
| Question | Answer |
|---|---|
| Chemical equations are always balanced. Explain why. (1 mark) | No atoms are lost/made (during a chemical reaction) or the atoms are rearranged (during a chemical reaction. Accept because of (the law of) conservation of mass/matter. |
| Why is sodium chloride a compound? (2 mark) | Two different types atoms/elements/ions are bonded/joined together. Do not accept different size. |
| Why is titanium an element? (1 mark) | All atoms are the same/it only contains one type of atom. Accept all ions are the same. |
| An atom of argon has 18 protons and 22 neutrons. Work out its atomic number and its mass number. (1 mark) | The atomic number is 18. The atomic mass is18 + 22 = 40. |
| Use ideas about electron arrangements to explain why the elements in Group 0 have similar properties. (2 marks) | The highest occupied energy level of each group 0 element contains 8 electrons. Because there are the same number of electrons in the highest occupied energy level of each group 0 element, the group 0 elements have similar properties. |
| How many elements join together to make the compound sodium chloride? (1 mark) | Two – sodium and chlorine |
| Use ideas about atoms to explain the difference between an element and a compound. (2 marks) | An element is made up of one type of atom only. A compound consists of atoms of more than one type. |
| Explain how sodium and chloride ions are formed when sodium chloride is made from its elements. (2 marks) | When sodium chloride forms from its elements, one electron is transferred from the sodium atom to the chlorine atom. This results in a sodium ion with a single positive charge, Na+, and a chloride ion with a single negative charge, Cl-. |
| Explain how the atoms in a carbon monoxide molecules are held together. (1 mark) | In carbon monoxide, electrons are shared between the carbon and oxygen atoms. |
| A molecule of sulphur trioxide consists of one atom of sulfur joined to three atoms of oxygen. Work out its formula. (1 mark) | SO3 |
| The formula of potassium manganate (VII) is KMnO4. Explain what the formula tells us about this compound. (2 marks) | In potassium manganate (VII) (potassium permanganate), there are four atoms of oxygen and one atom of manganese for every one atom of potassium. |
| Limestone is a hard rock that is used as a building material. Limestone was used by the Egyptians to make plaster. Use the reactions of the lime cycle to explain how the plaster became even harder with age. (3 marks) | - carbon dioxide / CO 2 - (carbon dioxide) reacts (with the calcium hydroxide / slaked lime / plaster) - limestone / calcium carbonate /Ca CO 3 forms - water is lost / evaporates |
Created by:
The Scientist
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