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The heat change when mole of substance is formed from its constituent elements in their standard state.
johnmulu answered the question on February 15, 2017 at 07:14
- State two factors that should be considered when choosing fuel for cooking(Solved)
State two factors that should be considered when choosing fuel for cooking.
Date posted: February 15, 2017. Answers (1)
- Butane and propane are constituents of cooking gas. Which one produces more energy per mole on combustion?(Solved)
Butane and propane are constituents of cooking gas. Which one produces more energy per mole on combustion? Explain.
Date posted: February 15, 2017. Answers (1)
- When pure water is heated at 1 atmospheric pressure at sea level, the temperature of the water does not rise beyond 100oC(Solved)
When pure water is heated at 1 atmospheric pressure at sea level, the temperature of the water does not rise beyond 100oC, even with continued heating. Explain this observation
Date posted: February 15, 2017. Answers (1)
- Distinguish between exothermic and endothermic reaction(Solved)
Distinguish between exothermic and endothermic reaction.
Date posted: February 15, 2017. Answers (1)
- Explain why the enthalapy of neutralization of ethanoic acid with sodium hydroxide is different from that of hydrochloric acid with sodium hydroxide(Solved)
Explain why the enthalapy of neutralization of ethanoic acid with sodium hydroxide is different from that of hydrochloric acid with sodium hydroxide.
Date posted: February 15, 2017. Answers (1)
- A compound whose general formula is M(OH)3 reacts as shown by the equation below(Solved)
A compound whose general formula is M(OH)3 reacts as shown by the equation below.
M(OH)3(s) + OH$^-_4$(aq) $\rightarrow$ M(OH)$^-_4$(aq)
M(OH)3(s) + 3H+(aq) $\rightarrow$ M3+(aq) + 3H2O(l)
a) What name is given to compounds which behave like M(OH)3 in the two reactions
b) Name two elements whose hydroxides behave like that of M.
Date posted: February 15, 2017. Answers (1)
- When magnesium burns in air, it forms a white solid and a grey-green solid. When a few drops of water are added to the mixture, a gas that turns red litmus paper blue is evolved. Identify the:(Solved)
When magnesium burns in air, it forms a white solid and a grey-green solid. When a few drops of water are added to the mixture, a gas that turns red litmus paper blue is evolved.
Identify the:
i) White solid
ii) Gas evolved and the gas
I) Name of gas
II) Use of the gas.
Date posted: February 15, 2017. Answers (1)
- Naturally occurring magnesium consists of three isotopes. 78.6%24Mg; 10%25Mg and 26Mg. Calculate to one decimal place, the relative atomic mass of magnesium(Solved)
Naturally occurring magnesium consists of three isotopes. 78.6%24Mg; 10%25Mg and 26Mg. Calculate to one decimal place, the relative atomic mass of magnesium.
Date posted: February 15, 2017. Answers (1)
- Describe how sodium carbonate is used to remove water hardness. (Solved)
Describe how sodium carbonate is used to remove water hardness.
Date posted: February 15, 2017. Answers (1)
- Dissolving of potassium nitrate in water is an endothermic process. Explain the effect of increase in temperature on the solubility of potassium nitrate(Solved)
Dissolving of potassium nitrate in water is an endothermic process. Explain the effect of increase in temperature on the solubility of potassium nitrate.
Date posted: February 15, 2017. Answers (1)
- Starting with zinc sulphate solution, describe how a sample of zinc oxide can be obtained(Solved)
Starting with zinc sulphate solution, describe how a sample of zinc oxide can be obtained.
Date posted: February 15, 2017. Answers (1)
- Aqueous hydrogen chloride reacts with potassium manganate (VII) to produce chlorine gas, while a solution of hydrogen chloride in methylbenzene has no effect on potassium manganate (VII)(Solved)
Aqueous hydrogen chloride reacts with potassium manganate (VII) to produce chlorine gas, while a solution of hydrogen chloride in methylbenzene has no effect on potassium manganate (VII). Explain this observation.
Date posted: February 15, 2017. Answers (1)
- (a) Name two cations that are present in hard water (b) Explain how the ion exchange resin softens hard water(Solved)
a) Name two cations that are present in hard water.
b) Explain how the ion exchange resin softens hard water.
Date posted: February 15, 2017. Answers (1)
- Describe how the presence of zinc ions and sulphate ions can be established(Solved)
A sample of river water is suspected to contain zinc and sulphate ions. Describe how the presence of zinc ions and sulphate ions can be established.
Date posted: February 15, 2017. Answers (1)
- Soap dissolves in water dissolves in water according to the equation below; NaSt(aq) $\rightarrow$ Na+(aq) + St- where St- is the stearate ion(Solved)
Soap dissolves in water dissolves in water according to the equation below; NaSt(aq) $\rightarrow$ Na+(aq) + St- where St- is the stearate ion.
a) Write the formula of the scum formed when soap is used in hard water.
b) Write the ionic equation for the reaction that occurs when sodium carbonate is used to remove hardness in water
Date posted: February 13, 2017. Answers (1)
- A sample of fertilizer is suspected to be calcium ammonium nitrate. Describe chemical test for each of the following ions in the sample(Solved)
A sample of fertilizer is suspected to be calcium ammonium nitrate. Describe chemical test for each of the following ions in the sample:
a) Calcium ions
b) Ammonium ions.
Date posted: February 13, 2017. Answers (1)
- For each of the following reactions, state the observation and write the formula of the compound responsible for the observation(Solved)
For each of the following reactions, state the observation and write the formula of the compound responsible for the observation:
a) Bromine water is added to aqueous potassium iodide
b) Excess aqueous ammonia is added to copper (II) hydroxide.
Date posted: February 13, 2017. Answers (1)
- Hardness of water may be removed by either boiling or addition of chemicals(Solved)
Hardness of water may be removed by either boiling or addition of chemicals.
a) Write an equation to show how boiling removes hardness of water.
b) Name two chemicals that are used to remove hardness of water.
Date posted: February 13, 2017. Answers (1)
- The elements nitrogen, phosphorous and potassium are essential for plant growth(Solved)
The elements nitrogen, phosphorous and potassium are essential for plant growth.
Potassium in fertilizers may be in the form of potassium nitrate.
Describe how a sample of a fertilizer may be tested to find out if it contained nitrate ions.
Date posted: February 13, 2017. Answers (1)
- Name two methods that can be used to remove permanent hardness from water(Solved)
Name two methods that can be used to remove permanent hardness from water.
Date posted: February 13, 2017. Answers (1)