Question

Calcium oxide is a base compound which can react with acids such as nitric acid, HNO3. A student mixed 1.5g of CaO with 2.5M HNO3. The chemical equation for this reaction is: CaO + HNO3 = Ca(NO3)2 + H2O. Solve the following questions?

Answer 1

Here's what I get.

Explanation:

a) Type of reaction

The chemical equation is

`"CaO" + "2HNO"_3 → "Ca"("NO"_3)_2 + 2"H"_2"O"`

In one sense, this is a double displacement reaction, because `"Ca"` and `"H"` are changing partners with `"O"` and `"NO"_3`.

In another sense, this is an acid-base neutralization reaction, because the base (calcium oxide) is reacting with the acid (nitric acid) to produce a salt (calcium nitrate) and water.

`underbrace("CaO")_color(red)("base") + underbrace("2HNO"_3)_color(red)("acid") → underbrace("Ca"("NO"_3)_2)_color(red)("salt") + underbrace(2"H"_2"O")_color(red)("water")`

b) Adding the base to the acid

(i) Using a a pH meter

At the start, the `"HNO"_3` will have a low pH, perhaps pH 1.

As you add the solid `"CaO"`, more of the acid will be neutralized and the solution will become more basic.

The pH will gradually increase, perhaps to pH 2.

As you get closer to complete neutralization, the pH will increase rapidly to pH and then to some higher value, perhaps pH 12.

As you continue adding `"CaO"`, the pH will slowly increase to pH 13 or higher.

If you were adding the `"CaO"` at a constant rate, a plot of pH vs time would look something like that below.

(Adapted from Chemistry Stack Exchange)

(ii) Using Universal Indicator

One type of Universal Indicator has the following colours.

Thus, you would probably start with an orange solution.

As you add `"CaO"`, the colour would change gradually to yellow, then rapidly through green to blue, and then slowly to a deep purple.