Question

Write the observations and balanced equations for the following reactions: Sodium hydroxide is added dropwise till in excess to a solution of zinc sulfate.

Answer 1

Hint: A chemical equation represents the substances that are involved in a chemical reaction i.e. reactants and products. The balanced chemical equation is the one that has the same number of atoms on both sides of a reaction.

Complete step by step answer:
When Sodium hydroxide is added dropwise till in excess to a solution of zinc sulfate. At first, a white precipitate of zinc hydroxide is formed. The reaction is shown below,
\[ZnS{O_4} + 2NaOH \to Zn{(OH)_{2}} + N{a_2}S{O_4}\;\]
But on the addition of an excess amount of sodium hydroxide the zinc hydroxide converted into sodium zincate. Sodium zincate is soluble in excess NaOH. so, the white precipitate will be dissolved. The reaction is shown below,
\[Zn{(OH)_{2}} + 2NaOH \to N{a_2}Zn{O_2} + 2{H_2}O\]

Additional information:
According to the law of conservation of mass, in an isolated system, mass is neither created nor destroyed by any chemical or physical transformations. There are examples of chemical reactions.
1.When Calcium carbonate reacts with hydrochloric acid, it produces calcium chloride and releases carbon dioxide gas. From this, we know that calcium carbonate and hydrochloric acid are the reactants and the products will be calcium chloride, carbon dioxide, and water.
\[CaC{O_3}(s) + HCl(aq) \to CaC{l_2}(aq) + C{O_2}(g) + {H_2}O\]
We can balance this equation by counting the particular atom on both sides and making them equal on each side. Calcium, carbon, and oxygen atoms are the same on both sides but hydrogen and chlorine atoms are double on the right side. Therefore, we get the balanced chemical equation by putting 2HCl on the left side as:
\[CaC{O_3}(s) + 2HCl(aq) \to CaC{l_2}(aq) + C{O_2}(g) + {H_2}O\]
2.When Dilute sulphuric acid reacts with zinc granules, it produces zinc sulphate and releases hydrogen gas. Because zinc is more reactive than hydrogen, it easily displaces hydrogen from sulphuric acid. This can be written in equation form as now we know the reactants and products.
\[{H_2}S{O_4}(aq) + Zn(s) \to ZnS{O_4}(aq) + {H_2}(g)\]
We can see that this reaction is already balanced. The number of atoms of zinc, sulphur, hydrogen, and oxygen is the same on both sides.

Note: We can easily measure the heat absorbed or evolved by a chemical reaction. Errors occur because some of the heat may escape before it can be measured – we need ideally to measure the total heat energy evolved or absorbed, which can be done if all the heat is transferred to a liquid whose temperature we measure, however, some heat is inevitably lost to the environment.