Problem 56 - Chemistry The Central Science

Question

Using the activity series (Table 4.5 ), write balanced chemical equations for the following reactions. If no reaction occurs, simply write NR. (a) Nickel metal is added to a solution of copper(II) nitrate; (b) a solution of zinc nitrate is added to a solution of magnesium sulfate; (c) hydrochloric acid is added to gold metal; (d) chromium metal is immersed in an aqueous solution of cobalt(II) chloride; (e) hydrogen gas is bubbled through a solution of silver nitrate.

Step-by-Step Solution

Answer

(a) \(Ni(s) + Cu(NO_3)_2(aq) \rightarrow Ni(NO_3)_2(aq) + Cu(s)\) (b) NR (c) NR (d) \(Cr(s) + 2CoCl_2(aq) \rightarrow 2Co(s) + CrCl_2(aq)\) (e) \(2AgNO_3(aq) + H_2(g) \rightarrow 2Ag(s) + 2HNO_3(aq)\)

Step 1: Use the activity series

In order to determine if a reaction will occur or not, we first need to consult the activity series of elements. From the table, the order of elements from the most to the least reactive is: K > Ca > Na > Mg > Al > Zn > Fe > Ni > Sn > Pb > H > Cu > Hg > Ag > Pt > Au. Now, let's discuss each subpart.

Step 2: (a) Nickel metal is added to a solution of copper(II) nitrate

Since Nickel (Ni) is more reactive than Copper (Cu), a reaction will occur. Using the activity series, we can deduce that Nickel will displace Copper from its nitrate solution: Ni(s) + Cu(NO3)2(aq) -> Ni(NO3)2(aq) + Cu(s)

Step 3: (b) A solution of zinc nitrate is added to a solution of magnesium sulfate

In this case, Zinc (Zn) is less reactive than Magnesium (Mg), so no reaction will occur. Thus, we simply write "NR."

Step 4: (c) Hydrochloric acid is added to gold metal

Gold (Au) is one of the least reactive metals, and Hydrogen (H) is relatively more reactive. So, no reaction will occur when hydrochloric acid (which contains hydrogen ions) is added to gold metal. Thus, we simply write "NR."

Step 5: (d) Chromium metal is immersed in aqueous solution of cobalt(II) chloride

Chrome (Cr) is more reactive than Cobalt (Co), so it will displace the latter from its chloride solution: Cr(s) + 2CoCl2(aq) -> 2Co(s) + CrCl2(aq)

Step 6: (e) Hydrogen gas is bubbled through a solution of silver nitrate

Hydrogen (H) is more reactive than Silver (Ag), so it will displace the latter from its nitrate solution: 2AgNO3(aq) + H2(g) -> 2Ag(s) + 2HNO3(aq) In summary, the balanced chemical equations for each subpart are: (a) Ni(s) + Cu(NO3)2(aq) -> Ni(NO3)2(aq) + Cu(s) (b) NR (c) NR (d) Cr(s) + 2CoCl2(aq) -> 2Co(s) + CrCl2(aq) (e) 2AgNO3(aq) + H2(g) -> 2Ag(s) + 2HNO3(aq)

Key Concepts

Reactivity of Metals

The reactivity of metals is a key concept in understanding how chemical reactions involving metals take place. Some metals are more reactive than others, and this reactivity is often compared using the activity series. This series orders metals from most reactive to least reactive, allowing us to predict which metals can displace others in compounds.
For example, a metal that's higher up in the series will replace a metal that's lower in a compound.

• Examples of highly reactive metals include Potassium (K) and Calcium (Ca), which can easily react with water and acids.
• In contrast, metals like Gold (Au) and Silver (Ag) are less reactive and won’t easily participate in reactions.

Understanding how metals react is essential for predicting the outcomes of reactions in chemical equations, like determining if nickel can displace copper as it is higher in the activity series.

Chemical Equations

Chemical equations are symbolic representations of chemical reactions, showing the reactants transforming into products. They provide information not only about the substances involved but also their proportions. Writing balanced chemical equations means ensuring the same number of each type of atom is present on both sides.
For instance, in the reaction between nickel and copper(II) nitrate, the equation will be:
\[ \text{Ni(s) + Cu(NO}_3\text{)}_2\text{(aq) → Ni(NO}_3\text{)}_2\text{(aq) + Cu(s)} \]
Here, one atom of nickel displaces copper, forming nickel nitrate and solid copper.

• Start by writing the unbalanced equation with the right formulas.
• Then, adjust coefficients to balance the equation, making sure atoms are conserved.

Balanced equations are crucial for accurate representation and understanding of a chemical process.

Predicting Reactions

Predicting whether a chemical reaction will occur involves understanding the nature of the substances involved and their reactivity. The activity series is a useful tool in making such predictions.
For example, if a more reactive metal is added to a solution containing a less reactive metal ion, a displacement reaction is likely to occur.

• In part (e), hydrogen gas bubbling through silver nitrate will result in silver being displaced, as hydrogen is more reactive according to the activity series.
• Conversely, in part (b), zinc nitrate and magnesium sulfate don't react because zinc is less reactive than magnesium.

Predicting reactions is not always straightforward but using the activity series to assess and compare reactivity is a powerful strategy in chemical analysis.