Question Video: Calculating the Concentration of Nitric Acid via Titrating against a Known Volume of Potassium Hydroxide Chemistry

A 30 mL solution of nitric acid was titrated against a 0.1 M solution of potassium hydroxide. The addition of 26.6 mL of potassium hydroxide was found to neutralize the nitric acid. What is the concentration of the nitric acid? Give your answer to 2 decimal places.

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Video Transcript

A 30-millimeter solution of nitric acid was titrated against a 0.1-molar solution of potassium hydroxide. The addition of 26.6 millimeters of potassium hydroxide was found to neutralize the nitric acid. What is the concentration of the nitric acid? Give your answer to two decimal places.

This question is asking us to perform a titration calculation. This means we’re going to need the equation 𝑛 equals 𝑐𝑣, where 𝑛 is the amount in moles, 𝑐 is the concentration in moles per liter, and 𝑣 is volume in liters. Let’s start by working out exactly what reaction is occurring here.

We’re told that we’re reacting nitric acid with potassium hydroxide. So this is an acid–base titration. Let’s finish writing out our reaction equation. When writing out our equation, we should check that it’s balanced. And luckily, it is. Now, let’s extract the important information from the question and put it into a table.

We’re told that we need 30 milliliters of nitric acid and 26.6 milliliters of potassium hydroxide. So these are our values for 𝑣. However, currently, they’re not in the units that we want. To convert milliliters to liters, we multiply by one liter per 1000 milliliters. By converting these values for 𝑣, we get 0.03 liters of acid and 0.0266 liters of potassium hydroxide. Next, we’re given the concentration of the potassium hydroxide as 0.1 molar. Remember that molar means moles per liter. And the question is asking us to work out the concentration of the nitric acid. So let’s fill in the boxes of our table until we can work this out.

First, we can work out the number of moles of potassium hydroxide. We do this by multiplying the concentration and the volume, giving us 0.00266 moles. But how do we know how many moles of acid we need? To work this out, we need to look at the molar ratio. We can see from our balanced chemical equation that both the nitric acid and the potassium hydroxide have a coefficient of one. This means we have a one-to-one molar ratio. So to neutralize one mole of acid, we need exactly one mole of potassium hydroxide.

But we have 0.00266 moles of potassium hydroxide instead. So this means that we need exactly the same number of moles of acid. Now that we have 𝑛 and 𝑣 for our acid, we can work out the concentration. We do the number of moles divided by the volume in liters, giving us 0.0887 molar. However, we’re asked for two decimal places. So our answer is 0.09 molar or moles per liter.

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