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Questions and Answers
What is the unit of charge and what is an equivalent combination of units?
What is the current in resistor R in the circuit shown?
Which diagram shows the outer electron arrangement in a molecule of carbon dioxide?
Which graph is the current-voltage characteristic of a filament lamp?
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Which statement is correct about the diagrams W, X, Y and Z?
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How much charge flows through a circuit in 1.5 minutes with a current of 100 mA?
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Which pure substance has the largest Rf value in the chromatogram?
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What is the new resistance of the wire after both its length and diameter are doubled?
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How does the resistance of a piece of wire depend on its cross-sectional area and on its length?
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What is true about compounds?
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What is component X in the circuit used for?
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What is the formula of cryolite?
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What is the formula of aluminium phosphate?
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What happens to the current in a circuit and the resistance of the wire when the length of the wire is doubled?
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Which two processes are used to separate the water from the chalk and salt?
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What type of bond holds atoms together in a compound?
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Which process is used to separate a mixture of coloured compounds?
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What is the smallest part of an element?
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What is formed when atoms of the same type chemically join together?
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What is the process of separating an insoluble impurity from an aqueous salt solution?
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How is the purity of an unknown solid substance assessed?
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What is the expression to calculate the efficiency of a machine?
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How much electric charge passes through a heater in one minute if there is a current of 6.0 A?
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Why is the extension block now dangerous if the 5 A fuse is replaced with a 13 A fuse?
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Which diagram shows the correct way to set up the apparatus for chromatography?
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In which order is the apparatus used to obtain pure copper sulfate?
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Study Notes
Chemistry
- A molecule of carbon dioxide has an outer electron arrangement represented by O=C=O with dots around O and X's around C.
- A compound is made up of two or more different elements chemically bonded together and cannot be broken down into simpler substances by physical processes.
- Compounds and their elements have different properties.
Diagrams
- A diagram showing the outer electron arrangement in a molecule of carbon dioxide is O=C=O with dots around O and X's around C.
- A diagram showing atoms and molecules can be represented by: W: (O—O—O), X: (O—O), Y: (O), Z: (O—O—O—O).
- A chromatogram shows the separation of four different substances.
Chemical Bonding
- Atoms are the smallest parts of elements, and when atoms of the same type chemically join together, a molecule is formed.
- When different types of atoms chemically join together, they form compounds.
Separation Techniques
- Filtration and crystallisation are used to separate a mixture of insoluble chalk and a soluble salt from water.
- Chromatography is used to separate a mixture of coloured compounds and to separate the colours in an ink.
- Distillation is used to separate a mixture of liquids with different boiling points.
Chemical Reactions
- Cryolite is a mineral which contains aluminium, sodium, and fluorine, with a formula of Na₃AlF₆.
- Sodium phosphate, Na₃PO₄, contains sodium ions, Na⁺, and aluminum sulfate, Al₂(SO₄)₃, contains sulfate ions, SO₄²⁻.
- The formula of aluminum phosphate is Al₂(PO₄)₃.
Physical Chemistry
- The purity of an unknown solid substance can be assessed by measuring its melting point.
- The efficiency of a machine can be calculated using the formula: (useful output energy / (useful output energy + wasted energy)) x 100%.
Electricity
- Electric charge can be calculated using the formula: Q = I x t, where Q is the charge, I is the current, and t is the time.
- The unit of charge is the coulomb (C), which is equivalent to an ampere-second (A s).
- The efficiency of a machine can be calculated using the formula: (useful output energy / (useful output energy + wasted energy)) x 100%.
Circuits
- Lamps in a lighting circuit in a house are connected in parallel, which allows them to be switched separately.
- A fuse is used to protect a circuit from excessive current, and a faulty fuse can be replaced with a new one of the same rating.
- A variable resistor is used to control the brightness of a lamp.
Resistance
- The resistance of a piece of wire depends on its length and cross-sectional area, with resistance being directly proportional to length and inversely proportional to cross-sectional area.
- The current in a circuit can be calculated using Ohm's law: I = V / R, where I is the current, V is the voltage, and R is the resistance.
Static Electricity
- When a plastic rod is rubbed with a dry woollen cloth, the rod becomes positively charged as electrons move from the cloth to the rod.
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Description
Test your understanding of molecular structure and diagrams with these questions about electron arrangement and atom representation. Identify the correct diagrams and statements about atoms and molecules.
