Question

14 multiple choice 1 point
which reaction types form a solid product?
neutralization reactions
precipitation reactions
gas - forming reactions
gas - forming reactions with a bicarbonate
15 multiple choice 1 point
an interesting precipitation reaction occurs when milk is combined with coca - cola. a key component of milk’s chemical makeup is calcium (ca). one component of coca - cola’s chemical formula is phosphoric acid ($h_3po_4$). what are the products of the molecular equation of a reaction between calcium and phosphoric acid?
$2ca_3(po_4) + 3h_2$
$ca_3(po_4)_2 + 3h_2$
$ca_3(po_4)_2 + 2h_2$
$ca_3(po_4)_2 + h_2$

Explanation:

Question 14

• Neutralization reactions form water and a salt (usually aqueous).
• Precipitation reactions involve the formation of an insoluble solid (precipitate) from aqueous reactants.
• Gas - forming reactions produce a gas, not a solid.
• Gas - forming reactions with a bicarbonate also produce a gas (e.g., CO₂), not a solid. So precipitation reactions are the ones that form a solid product.

Step 1: Identify the reaction type

Calcium (Ca) is a metal and phosphoric acid ($\ce{H_3PO_4}$) is an acid. This is a single - replacement reaction (metal displaces hydrogen from the acid). The general formula for the reaction of a metal (M) with an acid ($\ce{H_nX}$) is $\ce{M + H_nX -> M_{n}X + \frac{n}{2}H_2}$ (balancing for charge and atoms).

Step 2: Determine the charges and formula of the salt

Calcium has a charge of +2 ($\ce{Ca^{2+}}$) and the phosphate ion ($\ce{PO_4^{3 - }}$) has a charge of - 3. To form a neutral compound, we use the criss - cross method: the number of calcium ions is 3 (from the charge of phosphate) and the number of phosphate ions is 2 (from the charge of calcium), so the formula of calcium phosphate is $\ce{Ca_3(PO_4)_2}$.

Step 3: Balance the hydrogen gas

The reaction is $\ce{Ca + H_3PO_4 -> Ca_3(PO_4)_2 + H_2}$. First, balance the calcium and phosphate: 3 $\ce{Ca}$ atoms react with 2 $\ce{H_3PO_4}$ molecules. Then, for the hydrogen: from 2 $\ce{H_3PO_4}$ molecules, we have 6 H atoms, so the number of $\ce{H_2}$ molecules is 3 (since each $\ce{H_2}$ has 2 H atoms, 6/2 = 3). The balanced equation is $\ce{3Ca + 2H_3PO_4 -> Ca_3(PO_4)_2 + 3H_2}$. So the products are $\ce{Ca_3(PO_4)_2 + 3H_2}$.

Answer:

B. precipitation reactions

Question 15