Question

a chemical reaction is represented by the following word equation. zinc + lead(ii)nitrate -----> zinc nitrate + lead what type of chemical reaction is this reaction classified to? your answer indicate which of the following statements concerning ph is true or false. (4marks) a)a change of one unit on the ph scale (e.g., going from ph 9 to ph10 represents a doubling of the concentration of a base. __________ b)as the ph decreases, the solution becomes more basic. ________ (c)the definition of ph is: ph = -logh+ where h+ represents the mass of the acid in the solution. ________. d)a ph of 2 is 1000 times more acidic than a ph of 5. __________

Explanation:

First part (Chemical reaction type):

A single - displacement reaction is a reaction in which one element replaces another element in a compound. In the reaction \(zinc + lead(II)nitrate\to zinc nitrate + lead\), zinc (\(Zn\)) replaces lead (\(Pb\)) in lead(II) nitrate (\(Pb(NO_3)_2\)). The general form of a single - displacement reaction is \(A+BC\to AC + B\), where \(A\) is a more reactive element than \(B\). Here, \(Zn\) is more reactive than \(Pb\) (based on the reactivity series of metals).

Second part (pH statements):

a)

The pH scale is a logarithmic scale. The formula for pH is \(pH=-\log[H^+]\), and for pOH (related to base concentration) \(pOH =-\log[OH^-]\) and \(pH + pOH=14\). A change of one unit on the pH scale (e.g., from pH 9 to pH 10) represents a ten - fold change in the concentration of \(OH^-\) (base) because of the logarithmic nature (\(y = \log_{10}x\), if \(x_1\) and \(x_2\) are concentrations and \(y_1\) and \(y_2\) are pOH values, \(y_2-y_1=\log(x_2)-\log(x_1)=\log(\frac{x_2}{x_1})\), when \(y_2 - y_1 = 1\), \(\frac{x_2}{x_1}=10\)). So, the statement "A change of one unit on the pH scale (e.g., going from pH 9 to pH10 represents a doubling of the concentration of a base" is False.

b)

The pH scale ranges from 0 - 14. A lower pH (\(pH<7\)) means a higher concentration of \(H^+\) (more acidic) and a higher pH (\(pH > 7\)) means a higher concentration of \(OH^-\) (more basic). As the pH decreases (e.g., from pH 8 to pH 6), the concentration of \(H^+\) increases and the solution becomes more acidic. So, the statement "As the pH decreases, the solution becomes more basic" is False.

c)

The definition of pH is \(pH=-\log[H^+]\), where \([H^+]\) represents the molar concentration (moles per liter, \(mol/L\)) of hydrogen ions (\(H^+\)) in the solution, not the mass of the acid. So, the statement "The definition of pH is: \(pH =-\log[H+]\) where \([H+]\) represents the mass of the acid in the solution" is False.

d)

Using the formula \(pH=-\log[H^+]\), if \(pH_1 = 2\), then \([H^+]_1=10^{- 2}\space mol/L\), if \(pH_2 = 5\), then \([H^+]_2=10^{-5}\space mol/L\). The ratio \(\frac{[H^+]_1}{[H^+]_2}=\frac{10^{-2}}{10^{-5}}=10^{3} = 1000\). A lower pH means a higher concentration of \(H^+\) (more acidic). So, a pH of 2 is 1000 times more acidic than a pH of 5, and the statement is True.

Answer:

• First part: Single - displacement reaction
• Second part:
• a) False
• b) False
• c) False
• d) True