Chemistry: Molecular Structure and Diagrams

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Questions and Answers

What is the unit of charge and what is an equivalent combination of units?

ampere, volt ohm

coulomb, ampere/second (correct)

volt, ohm

ampere, coulomb second

What is the current in resistor R in the circuit shown?

1.8 A

0.20 A

0.40 A

0.60 A (correct)

Which diagram shows the outer electron arrangement in a molecule of carbon dioxide?

O=C=O with X's around O and dots around C

O=C=O with X's and dots around O and C

O=C=O with dots and X's around O and C

O=C=O with dots around O and X's around C (correct)

Which graph is the current-voltage characteristic of a filament lamp?

Graph A Signup and view all the answers

Which statement is correct about the diagrams W, X, Y and Z?

W, X, and Z are molecules and Y is an atom. Signup and view all the answers

How much charge flows through a circuit in 1.5 minutes with a current of 100 mA?

9.0 C Signup and view all the answers

Which pure substance has the largest Rf value in the chromatogram?

Substance D Signup and view all the answers

What is the new resistance of the wire after both its length and diameter are doubled?

2R Signup and view all the answers

How does the resistance of a piece of wire depend on its cross-sectional area and on its length?

directly proportional, inversely proportional Signup and view all the answers

What is true about compounds?

They are made up of two or more different elements, chemically bonded, and have different properties. Signup and view all the answers

What is component X in the circuit used for?

controlling brightness Signup and view all the answers

What is the formula of cryolite?

NaAl3F6 Signup and view all the answers

What is the formula of aluminium phosphate?

Al3(PO4)2 Signup and view all the answers

What happens to the current in a circuit and the resistance of the wire when the length of the wire is doubled?

decreases, increases Signup and view all the answers

Which two processes are used to separate the water from the chalk and salt?

Decantation and filtration Signup and view all the answers

What type of bond holds atoms together in a compound?

Chemical bond Signup and view all the answers

Which process is used to separate a mixture of coloured compounds?

chromatography Signup and view all the answers

What is the smallest part of an element?

atom Signup and view all the answers

What is formed when atoms of the same type chemically join together?

molecule Signup and view all the answers

What is the process of separating an insoluble impurity from an aqueous salt solution?

filtration then crystallisation Signup and view all the answers

How is the purity of an unknown solid substance assessed?

measuring its melting point Signup and view all the answers

What is the expression to calculate the efficiency of a machine?

(1000 - 300) / 1000 × 100% Signup and view all the answers

How much electric charge passes through a heater in one minute if there is a current of 6.0 A?

360 C Signup and view all the answers

Why is the extension block now dangerous if the 5 A fuse is replaced with a 13 A fuse?

The cable may overheat before the fuse blows. Signup and view all the answers

Which diagram shows the correct way to set up the apparatus for chromatography?

spot of ink on paper and solvent at bottom Signup and view all the answers

In which order is the apparatus used to obtain pure copper sulfate?

Bunsen burner, tripod and flask → filter funnel → crystallising dish Signup and view all the answers

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.