Lab 1b

Review: What gas contributes to the smell of your bottles?

• Hydrogen Sulfide

• Methane

• Carbon Dioxide

• Oxygen

Answer explanation

Methane doesn't have a smell -- that's why hydrogen sulfide is intentionally added to gas used for cooking -- so you can smell a leak!

Review: How do we calculate VS?

• (Dry weight - burnt weight)/total weight

• (Weight after 105C - Weight after 550 C)/(wet weight - tare weight)

• (Weight after 550C - Weight after 105 C)/(wet weight - tare weight)

• Mass/Volume

Answer explanation

VS, or volatile solids, are the solids that burn at 550C (organic matter), so we calculate them as the dry weight (after drying at 105C) minus the burnt weight (after burning at 550C) divided by the total weight (wet weight minus the weight of the tin, or the tare weight)

Review: What inoculum:substrate ratio did we use?

• 2:1 by volume

• 2:1 by VS

• 1:2 by volume

• 1:2 by VS

Answer explanation

We used volatile solids to get a 2:1 ratio of inoculum VS to substrate VS

What is alkalinity?

• The pH of a sample

• The ability of a sample to stay at the same pH when acid or base is added

• Buffer capacity

• The sum of bicarbonate, carbonate, and hydroxide in the system

Answer explanation

Alkalinity is the buffer capacity of a sample, or the ability to keep its pH when acid or base is added. In biological systems, this is primarily due to the bicarbonate, carbonate, and hydroxide species. It is not the pH itself, though, since a sample could have the ability to retain a very high or very low pH if it has high alkalinity.

What is a GC (for the purpose of this lab)?

• A graduated cylinder

• A gas chromatograph

• A tool used to measure the type of gas in a gas sample

• A goofy con-man

Answer explanation

A GC (for this lab) is a gas chromatograph, which is a machine that uses a heated column and carrier gas to determine the volumes of gas that burn at different temperatures -- this helps us identify the types of gas present and the composition of the combined gas!

How is pH measured with a pH probe?

• Voltage is measured and converted to pH

• The voltage potential between a sample and a reference electrode is used with temperature to determine pH

• The pH probe measures the color after a colorimetric reaction with the sample

• The pH probe adds acid and base and measures small reactions that occur

How is alkalinity measured?

• We can use an alkalinity probe to measure alkalinity

• Alkalinity is calculated by extracting carbonate, bicarbonate, and hydroxide and measuring the volume of each

• Alkalinity is calculated based on the amount and strength of acid needed to change the sample to pH 4.5

• Alkalinity is the amount of acid needed to get to a pH of 4.5