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Chemistry 1

Core Science Model Answers

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