a) There was no oxygen needed for rusting to take place since boiling water removes dissolved oxygen
b) i) Aluminium forms a tough oxide coating that protects iron from rusting.
ii) Alumium is more reactive than iron hence preferentially takes oxygen
johnmulu answered the question on April 6, 2017 at 13:19
- In an experiment, dry hydrogen gas was passed over heated Lead (II) Oxide as shown in the diagram below.
(Solved)
In an experiment, dry hydrogen gas was passed over heated Lead (II) Oxide as shown in the diagram below.
State and explain the observations made in the combustion tube
Date posted: April 6, 2017. Answers (1)
- The diagram below represents a set-up that was used to show that part of air is used during burning.(Solved)
The diagram below represents a set-up that was used to show that part of air is used during burning.
a) Given that phosphorus used was used in excess, draw a diagram of the set-up at the end of the experiment (when there was no further observable change).
b) Suggest one modification that should be made on the apparatus if the percentage of the air used is to be determined.
Date posted: April 6, 2017. Answers (1)
- Air was passed through several reagents as shown in the flow chart below(Solved)
Air was passed through several reagents as shown in the flow chart below
a) Write an equation for the reaction which takes place in the chamber with magnesium powder.
b) Name one gas which escapes from the chamber containing magnesium powder. Give reason for your answer.
Date posted: April 6, 2017. Answers (1)
- The diagram below is a set-up for the laboratory preparation of oxygen gas(Solved)
The diagram below is a set-up for the laboratory preparation of oxygen gas
a) Name solid R.
b) Write an equation for the reaction that takes place in the flask.
c) Give one commercial use of oxygen.
Date posted: April 6, 2017. Answers (1)
- The oxides of elements A and B have the properties shown in the table below. (the letters do not represent the actual symbols of elements)(Solved)
The oxides of elements A and B have the properties shown in the table below. (the letters do not represent the actual symbols of elements)
Give one example of elements A and B
Date posted: April 6, 2017. Answers (1)
- The diagram below shows an iron bar which supports a bridge. The iron bar is connected to a piece of magnesium metal.(Solved)
The diagram below shows an iron bar which supports a bridge. The iron bar is connected to a piece of magnesium metal.
Explain why it is necessary to connect the piece of magnesium metal to the iron bar.
Date posted: April 6, 2017. Answers (1)
- In an experiment a certain volume of air was passed repeatedly from syringe to syringe over heated excess zinc powder as shown in the diagram below.(Solved)
In an experiment a certain volume of air was passed repeatedly from syringe to syringe over heated excess zinc powder as shown in the diagram below.
The experiment was repeated using excess magnesium powder. In which of two experiments was the change in the volume of air greatest? Give reasons.
Date posted: April 6, 2017. Answers (1)
- The set-Up below was used to study some properties of air.(Solved)
The set-Up below was used to study some properties of air.
State and explain two observations that would be made at the end of the experiment.
Date posted: April 6, 2017. Answers (1)
- The diagram below represents a set-up that can be used to prepare and collect oxygen(Solved)
The diagram below represents a set-up that can be used to prepare and collect oxygen
a) Write an equation for the reaction that takes place.
b) What property of oxygen makes it possible for its collection as indicated by the diagram?
c) Explain why it is important not to collect any gas for the first few seconds of the experiment.
Date posted: April 6, 2017. Answers (1)
- A student added very dilute sulphuric (VI) acid to four substances and recorded the observations shown in the table below.(Solved)
A student added very dilute sulphuric (VI) acid to four substances and recorded the observations shown in the table below.
For which tests are the observations wrong? Explain.
Date posted: April 6, 2017. Answers (1)
- Study the diagram below and answer the questions that follow.(Solved)
Study the diagram below and answer the questions that follow.
Write an equation for each of the two reactions that takes place in the experiment represented by the diagram
Date posted: April 6, 2017. Answers (1)
- a) Explain what happens to the molecules of water in the region BC in terms of Kinetic theory.
b) In what state is the water in the region DE?
(Solved)
The graph below is a cooling curve for water. Study it and answer the questions that follow.
a) Explain what happens to the molecules of water in the region BC in terms of Kinetic theory.
b) In what state is the water in the region DE?
Date posted: April 6, 2017. Answers (1)
- The set up below was used to separate a mixture of methanol and propanol. Study it and answer the questions that follow.(Solved)
The set up below was used to separate a mixture of methanol and propanol. Study it and answer the questions that follow.
a) State the function of X.
b) Which liquid will collect first in the beaker? Given a reason.
Date posted: April 6, 2017. Answers (1)
- The chromatogram below was obtained from a contaminated food sample P. Contaminants Q,R,S and T are suspected to be in P. Use it to answer the following questions.(Solved)
The chromatogram below was obtained from a contaminated food sample P. Contaminants Q,R,S and T are suspected to be in P. Use it to answer the following questions.
a) Identify the contaminant in mixture P?
b) Which is the most soluble contaminant in P?
Date posted: April 6, 2017. Answers (1)
- Classify the following processes as either chemical or physical.(Solved)
Classify the following processes as either chemical or physical.
Date posted: April 6, 2017. Answers (1)
- The graph below is a cooling curve of a substance from gaseous state to solid state.(Solved)
The graph below is a cooling curve of a substance from gaseous state to solid state.
Give the name of the: a) Process taking place between to and t1
b) energy change that occurs between between t3 and t4
Date posted: April 6, 2017. Answers (1)
- Sample of urine from three participants F, G and H at an international sports(Solved)
Sample of urine from three participants F, G and H at an international sports meeting were spotted onto a chromatography paper alongside two from illegal drugs A1 and A2. A chromatogram was run using methanol. The figure below shows the chromatogram.
a) Identify the athlete who had used an illegal drug.
b) Which drug is more soluble in methanol?
Date posted: April 6, 2017. Answers (1)
- The graph below shows a curve obtained when water at 20o was heated for 15 minutes.(Solved)
The graph below shows a curve obtained when water at 20o was heated for 15 minutes.
a) What happens to the water molecules between points W and X?
b) In which part of the curve does a change of state occur?
c) Explain why the temperature does not rise between points X and Y.
Date posted: April 6, 2017. Answers (1)
- Study the properties of substances V2 and V4 in the table below and answer the questions that follows.(Solved)
a) Study the properties of substances V2 and V4 in the table below and answer the questions that follows.
a) Which of the substances are liquid at 24oC?
b) Describe how a mixture containing V2 and V4 can be separated.
Date posted: April 6, 2017. Answers (1)
- A piece of chromatography paper was spotted with coloured inks obtained from pens labeled 1 to 6. The diagram below show the spots after the chromatogram was developed.(Solved)
A piece of chromatography paper was spotted with coloured inks obtained from pens labeled 1 to 6. The diagram below show the spots after the chromatogram was developed.
a) Which two pens contained the same pigment?
b) Which pens contained only one pigment?
c) According to the chromatogram, which pigment are present in the ink of pen number 6?
Date posted: April 5, 2017. Answers (1)