Question

1. the mass spectrum represented to the right is most consistent with which of the following elements? a. eu b. gd c. tb d. dy 6. based on the mass spectrum of a pure element represented to the right, the average atomic mass of the element is closest to which of the following? a. 185.7 amu b. 186.0 amu c. 186.3 amu d. 186.9 amu ba²⁺(aq) + so₄²⁻(aq) → baso₄(s) 7 a student obtains a 10.0g sample of a white powder labeled as bacl₂. after completely dissolving the powder in 50.0ml of distilled water, the student adds excess na₂so₄(s), which causes a precipitate of baso₄(s) to form, as represented by the equation above. the student filters the baso₄(s), rinses it, and dries it until its mass is constant. which of the following scientific questions could best be answered based on the results of the experiment? a. is the na₂so₄(s) used in the experiment pure? b. is the bacl₂(s) used in the experiment pure? c. what is the molar solubility of bacl₂ in water? d. what is the molar solubility of baso₄ in water?

Explanation:

5.

Step1: Recall Eu atomic - mass range

Eu (Europium) has isotopes with atomic masses around 151 and 153 mainly.

Step2: Recall Gd atomic - mass range

Gd (Gadolinium) has isotopes with atomic masses in the range shown in the first mass - spectrum (peaks around 152 - 161).

Step3: Recall Tb atomic - mass range

Tb (Terbium) has a single stable isotope with atomic mass 159.

Step4: Recall Dy atomic - mass range

Dy (Dysprosium) has isotopes with atomic masses mainly around 160 - 164.

Step1: Identify isotopic masses and abundances

Let the isotopic masses be \(m_1 = 185\), \(m_2=187\) with relative abundances \(a_1 = 40\%\) and \(a_2 = 60\%\) respectively.

Step2: Use the formula for average atomic mass

The formula for the average atomic mass \(A\) is \(A=\sum_{i}m_i\times a_i\). So \(A = 185\times0.4+187\times0.6\).

Step3: Calculate the average atomic mass

\[

$$\begin{align*} A&=(185\times0.4)+(187\times0.6)\\ &=74 + 112.2\\ &=186.2\approx186.3\text{ amu} \end{align*}$$

\]

Step1: Analyze the reaction

The reaction is \(Ba^{2 +}(aq)+SO_4^{2 -}(aq)\to BaSO_4(s)\). The student starts with a sample of \(BaCl_2\) and reacts it with excess \(Na_2SO_4\) to form \(BaSO_4\) precipitate.

Step2: Consider the purpose of the experiment

By measuring the mass of the \(BaSO_4\) precipitate, the student can calculate the amount of \(Ba^{2+}\) in the original \(BaCl_2\) sample. If the calculated amount of \(BaCl_2\) based on the mass of \(BaSO_4\) is equal to the amount expected from the 10.0 g sample of \(BaCl_2\) (assuming it is pure), then the \(BaCl_2\) is pure. If not, it is impure.

Answer:

B. Gd

6.