ACS Analytical Chemistry Exam (Latest 2026/2027) – Q&A with Correct Answers With Rations| A+ Graded

ACS Analytical Chemistry Exam
(Latest 2026/2027) – Q&A with
Correct Answers With Rations| A+
Graded


Section 1: Statistics & Data Treatment (Questions 1-15)

Q1: A student measures the concentration of a solution five times and
obtains the following results (in ppm): 12.3, 12.5, 12.2, 12.4, 12.6. What is
the standard deviation of these measurements?

 A) 0.10
 B) 0.16
 C) 0.20
 D) 0.25

Correct Answer: B) 0.16
Rationale: The mean is 12.4. The variance is calculated
as s2=∑(xi−xˉ)2n−1=0.104=0.025s2=n−1∑(xi−xˉ)2=40.10=0.025 . The standard
deviation is the square root of the variance, s=0.025=0.158≈0.16s=0.025
=0.158≈0.16 ppm .

Q2: Which statistical test is appropriate for comparing the means of two
independent sample groups?

 A) Chi-square test
 B) Paired t-test

, C) Independent samples t-test
 D) ANOVA

Correct Answer: C) Independent samples t-test
Rationale: The independent samples t-test is used to determine if there is a
statistically significant difference between the means of two independent
groups. A paired t-test is for dependent samples, ANOVA for more than
two groups, and a chi-square test for categorical data .

Q3: A calibration curve has the
equation y=1.25x+0.02y=1.25x+0.02 with R2=0.998R2=0.998 . If a sample
gives a response of y=5.77y=5.77 , what is the concentration?

 A) 4.58
 B) 4.60
 C) 4.62
 D) 4.65

Correct Answer: B) 4.60
Rationale: Using the calibration equation, solve
for xx: 5.77=1.25x+0.02→x=5.77−0.021.25=5.751.25=4.605.77=1.25x+
0.02→x=1.255.77−0.02=1.255.75=4.60 .

Section 2: Spectroscopic Methods (Questions 16-30)

(Question 4 is provided as an example from this section.)

Q4: A mass spectrum of an organic compound shows a molecular ion peak
at m/z 150 and an M+2 peak of equal intensity. Which element is most
likely present?

 A) Chlorine
 B) Bromine

, C) Sulfur
 D) Nitrogen

Correct Answer: B) Bromine
Rationale: Bromine has two stable isotopes, 79Br79Br and 81Br81Br, which
occur in nearly equal abundance. This gives rise to an M and M+2 peak of
approximately equal intensity. Chlorine gives a 3:1 ratio, and sulfur's M+2
peak is much smaller (~4%) .


Section 3: Chromatographic Separations (Questions 31-45)

(Question 5 is provided as an example from this section.)

Q5: In gas chromatography, the retention factor k′k ′ for a compound is 5.0
on a column with a void time ( tMtM) of 2.0 min. What is the adjusted
retention time?

 A) 8.0 min
 B) 10.0 min
 C) 12.0 min
 D) 7.0 min

Correct Answer: B) 10.0 min
Rationale: The retention factor is defined as k′=tR−tMtMk ′=tMtR−tM.
Therefore, the adjusted retention time ( tR−tMtR−tM) is calculated
as k′×tM=5.0×2.0=10.0k ′×tM=5.0×2.0=10.0 min .


Section 4: Electroanalytical Techniques (Questions 46-55)

(Question 6 is provided as an example from this section.)

, Q6: For the reaction Cu2++2e−→Cu(s)Cu2++2e−→Cu(s),
if [Cu2+]=1.0×10−4M[Cu2+]=1.0×10−4M, what is the half-cell potential
relative to the standard hydrogen electrode? ( E∘=0.337VE∘=0.337V)

 A) 0.337 V
 B) 0.278 V
 C) 0.396 V
 D) 0.219 V

Correct Answer: D) 0.219 V
Rationale: Using the Nernst equation, E=E∘−0.0592nlog⁡QE=E∘−n0.0592
logQ. Here, n=2n=2 and Q=1[Cu2+]=104Q=[Cu2+]1=104.
So, E=0.337−0.05922log⁡(104)=0.337−0.1184=0.2186V≈0.219VE=0.3
37−20.0592log(104)=0.337−0.1184=0.2186V≈0.219V .

Section 5 & 6: Other Topics

(These are standalone questions covering statistical concepts, error, and
titration.)

Q7: What does ppm usually equal in aqueous solutions?

 A) mg/L
 B) μg/L
 C) ng/L
 D) g/L

Correct Answer: A) mg/L

Q8: Define accuracy.

 A) Closeness of the measured mean to the true value
 B) Reproducibility of individual measurements