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Quizzes > Science

Serial Dilution Practice Problems Quiz

Quick, free dilution calculation quiz. Instant results.

Editorial: Review CompletedCreated By: Erik LarsenUpdated Aug 25, 2025
Difficulty: Moderate
2-5mins
Learning OutcomesCheat Sheet
Paper art lab tubes and droplets on coral background for serial dilution calculations practice quiz

This quiz helps you tackle serial dilution practice problems, compute tube-by-tube factors, and check your setup before lab or exams. If you need a refresh on solution basics, try the solutions practice test, then build pH intuition with buffer solution practice problems. To tighten measurements that affect dilutions, see the accuracy and precision quiz.

What is the dilution factor when you dilute 1 mL of stock solution into 9 mL of diluent?
1:9
1:100
10:1
1:10
The dilution factor equals the volume of stock divided by the total volume. In this case, 1 mL stock plus 9 mL diluent gives a total of 10 mL, so the stock is diluted 1 part in 10 parts. This is commonly called a tenfold or 1:10 dilution. .
If a solution is diluted to 10^-3 of its original concentration, what percentage of the original concentration remains?
0.01%
0.001%
1%
0.1%
A dilution to 10^-3 means the final concentration is 0.001 times the original. Converting this to a percentage involves multiplying by 100, resulting in 0.1%. Thus only one tenth of one percent of the original concentration remains after a 10^-3 dilution. .
How would you prepare a 1/100 (10^-2) dilution using a single transfer?
10 mL stock + 90 mL diluent
0.1 mL stock + 9.9 mL diluent
1 mL stock + 9 mL diluent
1 mL stock + 99 mL diluent
A 1/100 dilution means the stock is 1 part in 100 parts total. To achieve this, you mix 1 mL of stock with 99 mL of diluent for a final volume of 100 mL. Other combinations change the dilution factor. .
How many times more dilute is a 10^-6 dilution compared to a 10^-3 dilution?
1000-fold
10-fold
10000-fold
100-fold
A 10^-6 dilution is 10^-6 divided by 10^-3 = 10^-3, which equals a 1/1000 ratio. Thus the 10^-6 dilution is 1,000 times more dilute than a 10^-3 dilution. This is a straightforward comparison of exponents. .
You need to prepare a 10^-5 dilution by performing consecutive 1:10 dilutions. How many serial dilution steps are required?
4
3
5
10
Each 1:10 dilution reduces concentration by one order of magnitude. To reach 10^-5, you need five tenfold dilutions (10^-1 × 10^-1 × 10^-1 × 10^-1 × 10^-1 = 10^-5). Fewer steps won't reach the desired dilution. .
After performing 1:10 serial dilutions across multiple tubes, the sample in the fourth tube has what overall dilution factor?
10^-3
10^-4
10^-1
10^-2
The first tube gives 10^-1, the second 10^-2, the third 10^-3, and the fourth 10^-4. You multiply the dilution factors sequentially for each step. This pattern holds for any series of equal dilutions. .
If you transfer 0.5 mL of sample into 4.5 mL diluent for each 1:10 dilution, how many rounds are needed to achieve a 10^-6 dilution?
4
5
6
7
Each transfer creates a 1:10 dilution (0.5 mL sample + 4.5 mL diluent). To reach an overall factor of 10^-6, you need six consecutive tenfold steps. Five steps only give 10^-5. .
To prepare 1 mL of 10^-4 M from a 1 M stock, which dilution scheme is correct?
Dilute 1 ?L into 999 ?L, then 10 ?L into 990 ?L
Dilute 1 ?L into 999 ?L (1:1000), then 1 ?L into 9 ?L (1:10)
Dilute 10 ?L into 990 ?L, then 10 ?L into 990 ?L
Dilute 100 ?L into 900 ?L, then 10 ?L into 990 ?L
To go from 1 M to 10^-4 M, you need a 10,000-fold dilution. Two 1:100 steps (10 ?L stock + 990 ?L diluent twice) multiply to 10^2 × 10^2 = 10^4. Other schemes do not achieve the correct total factor. .
What is the overall dilution factor when you perform a 1:5 dilution followed by a 1:20 dilution?
1:100
1:15
1:25
1:400
Dilution factors multiply when done in sequence. A 1:5 step followed by 1:20 gives 5 × 20 = 100, so the overall factor is 1:100. Always multiply each individual factor. .
To achieve a 10^-7 dilution using a combination of 1:100 and 1:10 steps, which sequence is appropriate?
One 1:1000 dilution followed by four 1:10 dilutions
Three 1:100 dilutions and one 1:10 dilution
Seven 1:10 dilutions
Two consecutive 1:100 dilutions followed by two consecutive 1:10 dilutions
Two 1:100 steps give 10^4, and two 1:10 steps give 10^2, yielding 10^4 × 10^2 = 10^6. Actually, to reach 10^-7 you need 10^7 total dilution, so two 100-fold and two 10-fold steps yield 10^2 × 10^2 × 10^1 × 10^1 = 10^6, which is incorrect. The proper approach is three 1:100 dilutions and one 1:10 dilution (100^3 × 10 = 10^7). .
If 80 colonies are counted from plating 0.1 mL of a 10^-6 dilution, what is the CFU/mL in the original sample?
8 × 10^8
8 × 10^7
8 × 10^6
8 × 10^9
CFU/mL = (colonies) ÷ (volume plated in mL) ÷ (dilution factor). Here that is 80 ÷ 0.1 ÷ 10^-6 = 80 × 10 × 10^6 = 8 × 10^8 CFU/mL. This converts the plated volume and accounts for dilution. .
To obtain 2 mL of a 10^-3 solution from stock, which pipetting protocol is correct?
Add 200 ?L of stock to 1800 ?L diluent
Add 20 ?L of stock to 1980 ?L diluent
Add 2 ?L of stock to 1998 ?L diluent
Add 0.2 ?L of stock to 1999.8 ?L diluent
A 10^-3 dilution in 2 mL total volume requires 0.002 mL (2 ?L) of stock and 1.998 mL diluent. Other volumes either under- or overshoot the desired factor. Precision is key for accurate dilutions. .
If each pipetting step has a relative error of 1%, what is the approximate total error after five serial 1:10 dilutions?
2.2%
5.1%
6%
5%
When errors propagate through multiplicative steps, you use the root-sum-square method: ?(n×error^2). Here ?(5×0.01^2)=0.02236 or about 2.2% total error. Simple summation would overestimate uncertainty. .
A sample is serially diluted 1:7, then 1:5, then 1:2. You plate 0.2 mL from the final dilution and count 50 colonies. What is the original concentration in CFU/mL?
2.5 × 10^4
5.0 × 10^3
3.5 × 10^5
1.75 × 10^4
Overall dilution = 7 × 5 × 2 = 70. The plated volume is 0.2 mL, so colonies per mL at that dilution = 50 ÷ 0.2 = 250. Multiply by 70 to revert to the original: 250 × 70 = 17,500 CFU/mL or 1.75 × 10^4. .
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Study Outcomes

  1. Calculate Dilution Factors -

    Apply mathematical formulas to determine the dilution factor at each step in a serial dilution practice problems scenario.

  2. Prepare Serial Dilution Series -

    Execute accurate pipetting and mixing techniques to construct a series of dilutions from a stock solution.

  3. Analyze Solution Concentrations -

    Interpret the resulting concentrations in each tube and confirm they meet the target values.

  4. Troubleshoot Experimental Errors -

    Identify common sources of error in serial dilution problems and implement corrective measures to improve accuracy.

  5. Evaluate Lab Technique Precision -

    Assess your pipetting consistency and precision when tackling serial dilutions practice problems in a lab setting.

  6. Interpret Practice Quiz Results -

    Review quiz feedback to understand your strengths and areas for improvement in serial dilution practice problems.

Cheat Sheet

  1. Master the C1V1 = C2V2 Formula -

    All serial dilution practice problems hinge on the formula C1V1 = C2V2, so practice rearranging it to solve for either V1 or C2 when you know the other three variables. For example, to make 5 mL of a 1:50 dilution from a 10 mM stock, calculate V1 = (C2×V2)/C1 = (0.2 mM×5 mL)/10 mM = 0.1 mL. Keep the mnemonic "copy the concentration and swap the volumes" handy for your next quiz.

  2. Calculate Cumulative Dilution Factors -

    In serial dilutions practice problems, obtain the total dilution by multiplying each step's individual factor (e.g., two 1:10 steps give 1:100, since 10 × 10 = 100). This "chain them, multiply them" approach is key when you design multi-step assays in university protocols. Remembering that a 1:2 followed by a 1:5 equals a 1:10 overall can save you time and errors in the lab.

  3. Optimize Pipetting Technique -

    Accurate pipetting is critical in serial dilution problems; always pre-wet tips by aspirating and dispensing the solution three times to ensure consistent volume delivery. Choose a pipette whose range centers on your target volume (for instance, use a P100 for transfers of 20 - 100 µL) to minimize relative error. These tips, drawn from reputable university lab guides, boost your confidence in every pipetting step.

  4. Design Clear Dilution Schemes -

    Select a dilution pattern - commonly 2-fold, 5-fold or 10-fold - based on your assay's sensitivity and concentration range. A 10-fold series (1:10, 1:100, 1:1000…) can be memorized as "ten, hundred, thousand!" to reinforce consistency in practice serial dilution problems. Sketching your tube layout on paper first helps prevent mix-ups and ensures full coverage of desired concentrations.

  5. Interpret Data with Logarithmic Plots -

    Plotting the log of concentration against your measured signal linearizes many dose - response relationships, making parameter extraction like EC50 straightforward, per NIH and journal protocols. Label axes clearly to match your serial dilutions practice problems and ensure reproducibility. This graphing approach turns complex dilution data into intuitive straight lines for easier analysis.

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