LO 4.5 - Specific Conductivity/Salt concentration

Question 1

Question

What is Specific Conductivity (SC)?

Specific conductivity (SC)

Answer 1

Specific conductivity assesses the total ions in a solution, not just the hydrogen ions.

With pH, we are only interested in the number of hydrogen ions.

Specific conductivity (SC)

Question 2

Question

How is Specific Conductivity (SC) assessed?

Specific conductivity (SC)

Answer 2

SC is assessed by measuring the ability of the solution to conduct an electrical charge.

Specific conductivity (SC)

Question 3

Question

How is Specific Conductivity (SC) measured?

Specific conductivity (SC)

Answer 3

Most commonly measured in milliSiemens/cm or microSiemens/cm.

Specific conductivity (SC)

Question 4

Question

What is a Siemen in relation to SC?

Specific conductivity (SC)

Answer 4

A Siemen is a unit of electrical conductance.

Specific conductivity (SC)

Question 5

Question

What is the Specific Conductivity (SC) reading of Pure water?

Specific conductivity (SC)

Answer 5

Pure water has no ions in it and will have an SC reading of (virtually) zero.
Typical values in S (mS in brackets):
* Pure water : 0.05

Specific conductivity (SC)

Question 6

Question

What is the Specific Conductivity (SC) reading of distilled water?

Specific conductivity (SC)

Answer 6

Typical values in uS (mS in brackets):
* Distilled water : 0.5

Specific conductivity (SC)

Question 7

Question

What is the Specific Conductivity (SC) reading of domestic tap water?

Specific conductivity (SC)

Answer 7

Typical values in uS (mS in brackets):
* Domestic tap water : 500 - 800 (0.5 - 0.8)

Specific conductivity (SC)

Question 8

Question

What is the Specific Conductivity (SC) reading of sea water?

Specific conductivity (SC)

Answer 8

Typical values in uS (mS in brackets):
* Sea water : 56,000 (56)

Specific conductivity (SC)

Question 9

Question

Compare the SC of mains supply vs well water.

Specific conductivity (SC)

Answer 9

Water taken from the mains supply, or from a well, will contain variable amounts of ions.

Specific conductivity (SC)

Question 10

Question

How does hard and soft water relate to SC?

Specific conductivity (SC)

Answer 10

‘Hard’ water has a higher concentration of ions and so will have a higher SC reading than ‘soft’ water.

Specific conductivity (SC)

Question 11

Question

What effect does adding fertiliser have on SC?

Specific conductivity (SC)

Answer 11

Adding nutrients in the form of fertiliser increases the concentration of ions and so increases the SC.

Specific conductivity (SC)

Question 12

Question

SC in nurseries, some points to note.

three points.

Specific conductivity (SC)

Answer 12

• In nurseries, SC is measured on a regular basis to monitor the levels of ions in feed solutions and in extracts taken from growing media.
• The SC of the water source also needs to be taken into account as this will affect the readings.
• Regular monitoring of SC allows the grower to adjust the concentration of fertiliser to be applied.

Specific conductivity (SC)

Question 13

Question

Samples of compost are mixed with water – the resulting liquid is tested.

Specific conductivity (SC)

Answer 13

• Depending on the crop and the growth stage, the grower might determine that when the SC rises above a certain figure, the next irrigation will be with plain water rather than a liquid feed.

Specific conductivity (SC)