Video: GCSE Chemistry Higher Tier Pack 1 • Paper 1 • Question 1

GCSE Chemistry Higher Tier Pack 1 • Paper 1 • Question 1

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Video Transcript

Table one shows the melting points and colours in aqueous solution of four transition elements in period four of the periodic table. Why does nickel have a higher melting point than copper? Tick one box. The covalent bonds between nickel atoms are stronger. The metallic bonds between nickel atoms are stronger. Nickel is more reactive than copper. Nickel ions are more highly charged than copper ions.

The first thing you might want to do is just reassure yourself that nickel does in fact have a higher melting point than copper. We can see from table one that nickel has a melting point of 1455 degrees C, which is a good deal more than copper at 1085 degrees C. Now a higher melting point suggests that more energy is required in order to break up the bonds between the constituents. This suggests that the answer will have something to do with the bonding involved in nickel and copper. Let’s go through the statements one by one.

The covalent bonds between nickel atoms are stronger. This statement is invalid because nickel and copper are both metals and therefore have metallic bonding between their atoms, not covalent bonding. The metallic bonds between nickel atoms are stronger. This statement is the correct answer. Stronger bonds in nickel mean that more energy is required to melt it, which means it will have a higher melting point.

Just to be safe, let’s look at the last two statements. Nickel is more reactive than copper. This statement is true, but it is not the correct answer. Something like sodium, which is even more reactive than nickel and copper, has a much lower melting point. The relationship between reactivity and melting point just isn’t that simple. Nickel ions are more highly charged than copper ions. This statement is false. Nickel ions and copper ions are both commonly found with a two plus charge.

Therefore, the answer to “Why does nickel have a higher melting point than copper?” is the metallic bonds between nickel atoms are stronger.

Predict the melting point of cobalt. In normal circumstances, it will be very difficult to predict the melting point of a metal without further data. Fortunately, there are clues within the question that will help you figure it out.

Iron, cobalt, nickel, and copper are all transition elements in the same period of the periodic table. Groups and periods in the periodic table show elements with similar chemical and physical properties. Since iron, cobalt, nickel, and copper are in the same period, they are likely to have a trend in their melting points. Let’s have a look.

Firstly, let’s remind ourselves of what a period is in the periodic table. This is a period on the periodic table. It’s the same as a row. And here, we find iron, cobalt, nickel, and copper next to one another. Since they are neighbours, they are likely to have a consistent trend in their melting points.

Let’s start by plotting the melting points from table one, and here they are. Overall, we can see that there’s a rough downward trend to the data, meaning that as we go from left to right across period four in the transition elements, the melting points should decrease. Let’s zoom in a little.

Given a downward trend, we expect that cobalt will have a melting point somewhere in between iron and nickel. Here’s the range. Without further information, the most sensible choice for a melting point will be the middle of this range. The easiest way to calculate the midpoint of a range is calculate the average of the two extremes.

Therefore, the melting point of cobalt is equal to the melting point of iron plus the melting point of nickel divided by two. This is equal to 1538 plus 1455 divided by two, which is equal to 1496.5 degrees C. All the values in the table are rounded to the nearest degree C, so our answer should be also. Therefore, the prediction for the melting point of cobalt is 1497 degrees C. Thankfully, this is very close to the real value of 1495 degrees C. This is a good prediction. However, you didn’t have very much data to work with. Therefore, anything in the range of 1475 degrees C to 1520 would’ve been acceptable.

A redox reaction occurs when solid iron is added to an aqueous solution of copper(II) chloride. The equation for this reaction is Fe solid plus CuCl₂ aqueous react to form FeCl₂ aqueous plus Cu solid. What is the colour of the solution at the end of the reaction if all of the copper(II) chloride reacts? Tick one box. Blue, blue-green, pink, green.

The first thing to note is that we are looking for the colour of the solution. And therefore, we can eliminate any solids. The question also says that all of the copper(II) chloride reactant reacts. Therefore, we can eliminate that as well. What we are left with is iron chloride in solution.

Therefore, the question can be rephrased as “What is the colour of iron(II) in solution?” Thankfully, you need not remember this from scratch. You can look at table one. In table one, the colour in aqueous solution of iron is listed as green. Therefore, the answer is green.

What is the ionic equation for the reaction of iron with copper(II) chloride solution? Tick one box. Fe²⁺ solid plus 2Cl⁻ aqueous react to form FeCl₂ aqueous, Fe solid plus Cl₂ aqueous react to form FeCl₂ aqueous, Fe solid plus Cu²⁺ aqueous react to form Fe²⁺ aqueous plus Cu solid, Fe solid plus Cu⁺ aqueous react to form Fe⁺ aqueous plus Cu solid.

The first thing to note about this question is that we are looking for an ionic equation. A net ionic equation has no spectator ions. Secondly, the reactants will be iron solid with copper(II) chloride solution. It’s the iron and the copper that are reacting; therefore, we expect to see Cu²⁺ ions in the reactants.

Let’s look at the statements one by one. Fe²⁺ solid plus 2Cl⁻ aqueous reacts to form FeCl₂ aqueous. This statement is incorrect because Fe²⁺ cannot be a solid. Secondly, there will be spectator ions in this equation if we expand out the FeCl₂. Since the Cl⁻ ions will appear on both sides of this equation, it will be classed as a spectator ion.

Fe solid plus Cl₂ aqueous react to form FeCl₂ aqueous. This statement is also invalid because Cl₂ was not listed as one of the reactants. Fe solid plus Cu²⁺ aqueous reacts to form Fe²⁺ aqueous plus Cu solid. This statement is the correct answer. It has no spectator ions. It has Fe solid and it has Cu²⁺ aqueous.

Let’s look at the last statement just to be safe. Fe solid plus Cu⁺ aqueous reacts to form Fe⁺ aqueous plus Cu solid. In this net ionic equation, the copper has the wrong charge. Therefore, this statement is incorrect.

Therefore, the answer to “What is the ionic equation for the reaction of iron with copper(II) chloride solution?” is Fe solid plus Cu²⁺ aqueous react to form Fe²⁺ aqueous plus copper solid.

Why is an aqueous solution of copper(II) chloride electrically conductive? Tick one box. It contains mobile ions. It contains water. It contains a metal. It contains mobile molecules.

Firstly, what is it that makes a liquid conductive? A conductive liquid is one that will allow charge to move between electrodes when placed inside. In order to conduct, there must be agents inside the liquid that can carry charge. These must therefore be charged themselves.

What do we have in a solution of copper(II) chloride that carries charge? The ions. We have the positively charged Cu²⁺ ions, which move to the negative electrode, and the negatively charged Cl⁻ ions, which move to the positive electrode. Therefore, the answer is, it contains mobile ions.

But let’s look at the other statements just to be sure. It contains water. This statement is not sufficient because pure water does not conduct electricity. It contains a metal. Well, placing a metal inside a liquid doesn’t suddenly make it conductive. Therefore, this statement is not true. It contains mobile molecules. Well, copper(II) chloride is an ionic solid, not a molecular solid. Therefore, this statement is invalid. Therefore, the answer to “Why is an aqueous solution of copper(II) chloride electrically conductive?” is, it contains mobile ions.

Which two substances are produced in the electrolysis of copper(II) chloride? Tick one box. Chlorine at the anode, hydrogen at the cathode, hydrogen at the anode, chlorine at the cathode, chlorine at the anode, copper at the cathode, copper at the anode, chlorine at the cathode.

Firstly, what’s it mean when you electrolyse copper(II) chloride? Copper(II) chloride is ionic. When it is electrolysed, its ions are oxidised or reduced back to its constituent elements. For Cu²⁺, that means turning it into copper solid. For Cl⁻, that means turning it into chlorine gas.

Now there’s just a question of whether these appear at the anode or the cathode. Let’s write the half equations in full. A Cu²⁺ ion requires two electrons to be turned into a copper solid atom. Two chloride ions each give up one electron in order to form a molecule of chlorine gas.

If you remember OILRIG, you should remember that oxidation is loss of electrons and reduction is gain of electrons. Here, the copper is gaining electrons. Therefore, this is a reduction. And the chloride are giving up electrons or losing electrons. Therefore, this is an oxidation.

Going back to the definitions of anode and cathode, an anode is where the oxidation occurs. You can remember this because “oxidation” and “anode” both have an A in them. The cathode is where reduction occurs. You can remember this because “cathode” and “reduction” both have a C in them.

So at the anode where oxidation occurs, we would expect chloride ions to be oxidised to chlorine. And at the cathode, we would expect Cu²⁺ ions to be reduced to copper. Therefore, the answer to “Which two substances are produced in the electrolysis of copper(II) chloride?” are chlorine at the anode and copper at the cathode.

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