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Michał T.
Molecular Biologist/Lab Tech
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Chemistry
TutorMe
Question:

How many moles of nitrogen are there in 35,4 dm^3 in normal conditions and what is the mass of it?

Michał T.
Answer:

In order to solve this problem, we need to remember that the volume of 1 mole of gas in normal conditions equals 22,4dm^3. Having this value, we can proceed with calculations. First, we establish a proportion related to our problem, we already now that; 1 mol of nitrogen => 22,4dm^3 Underneath, we substitute an x of moles, as unknown for the "how many moles" phrase, concluding this proportion; 1 mol of nitrogen => 22,4dm^3 x mol of nitrogen => 35,4dm^3 Now we calculate as follows; x = (35,4dm^3 * 1 mol)/22,4dm^3 x = 1,58 moles of nitrogen With the known number of moles of nitrogen, we can recalculate it into mass, by rearranging the formula for molecular mass "M = m/n", where m is the actual mass of the chemical (weighed out for a reaction for example), and n is the number of moles. We know the number of moles of nitrogen (just calculated above) and we know the molecular mass "M", because we can read it from the periodic table of elements, it equals 14 g/mol for a SINGLE atom of nitrogen. IMPORTANT: EVERY GAS, EXCEPT FOR NOBLE GASES, EXISTS IN A MOLECULAR FORM CONSISTING OF TWO ATOMS. That means or actual value of molecular mass for nitrogen will be twice as that, which is 28 g/mol. Now we can rearrange the formula for our purpose and calculate the mass of nitrogen: M = m/n | *n m = M*n m = 28 g/mol * 1,58 moles m = 44,24 grams This concludes our problem, and we can answer the question: There are 1,58 moles of nitrogen in 35,4dm^3 in normal condition and its mass equals 44,24 grams.

Basic Chemistry
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Question:

What is the definition of pH and what to we use it for?

Michał T.
Answer:

The exact definition of pH goes as following: "pH is the negative logarithm of the concentration of [H+] or [H30+] ions", but that is hard to understand for new chemists and this definition covers more complexed calculations. The easier to understand explanation is simply that pH gives us information about acidity or alkalinity of the solution. All we have to remember are two rules: -the lower the pH, the higher the acidity of the solution (strong acids such as concentrated sulfuric acid, hydrochloric acid, nitric acid) -the higher the pH, the higher the alkalinity (strong bases such as sodium hydroxide, potassium hydroxide, lithium hydroxide)

Biology
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Question:

What is the principle of Polymerase Chain Reaction (PCR) and what are the steps of it?

Michał T.
Answer:

Polymerase Chain Reaction (PCR) is a reaction of copying multiple DNA strands, starting from a template strand. It is called a chain reaction, because every product of the single reaction becomes the substrate for the following ones, thus, in the first cycle (see steps below), we have 4 strands of DNA (because the DNA is double stranded and we produced another strand on each of the two), then 8, 16, 32 and so on. PCR is widely used in molecular biology laboratories for genotyping (amplification of a specific gene to see if some kind of feature occurs in examined tissue/sample), production of DNA inserts for genetic engineering and many more. For each PCR you need a buffer to establish optimal reaction conditions, polymerase (the enzyme which builds a new strand using nucleotides from dNTP), dNTP mixture (a source of A, G, T, C nucleotides, just like building bricks for new DNA strand), forward and reverse primers (most frequently oligonucleotides which attach to the template strand and maintain a starting point for the polymerase) and the DNA template to start the copying procedure with. The PCR steps are as following: 1. Initial denaturation (opening the double stranded template DNA into single strands, to make a copy on each of the two) at 98 degrees Celcius - that is the temperature DNA gets denaturated. 2. Start of the cycle - the first and every other cycle goes as following (times may vary depending on different protocols): -denaturation of DNA at 98 degrees Celsius for ~10 seconds -annealing of forward (5' to 3') and reverse (3' to 5') primers at primer specific temperature for ~30 seconds -extension of new DNA strand which started from the primer binding site at 72 degrees Celsius for ~45 seconds 3. End of the cycle. 4. Repetition of the cycle (step 2-3) as many times as the procedure says, most frequently a regular PCR consists of 30-35 cycles. This may vary depending on the needs (more produced DNA needed, sample limitations etc.). 5. After all the cycles are completed, another extension at 72 degrees Celsius is carried out for ~5 minutes to ensure that there are ONLY double strands left. 4. Incubation of DNA at a suitable temperature, which is often 4 degrees Celsius.

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