Answer no 1)
The correct option is A) He did not try to learn it. It was natural.
As Sergei did not put any effort in learning the art of tongue rolling, hence we can assume that this characteristic was found to be naturally present in Sergei. This hence shows that Sergei has acquired the characteristic of tongue rolling through inheritance.
Answer No 2)
We can learn whether other persons in the class have the characteristic of tongue rolling or not by observing them. In the students who can roll their tongue we can conduct a survey asking them whether they tried to learn the trait or did not put any effort to learn tongue rolling. The students who learned the skill by practicing might have acquired the characteristic from learning.
Answer No 3)
We can survey the class for features like eye color, hair color, height, weight. We can ask certain questions in our survey like whether the characteristic can be seen in either the mother, father or other siblings.
Seems correct. Your steps make sense, the molar ratios are right and you've done it in a clear easy to follow manner. I see no issues with it.
Answer:
pH = 8.477
Explanation:
∴ ni 0.3 - -
nf - 0.3 0.3
∴ ni 0.50 - 0.3
nf 0.5 - X X 0.3 + X
∴ Ka = 2.0 E-9 = ([H3O+]*[OBr-]) / [HOBr]
⇒ Ka = 2.0 E-9 = ((X/1L)*(0.3 + X)/1 L) / ((0.5 - X)/1L)
⇒ 2.0 E-9 = ( 0.3X + X² ) / (0.5 - X)
⇒ X² + 0.3X - 1 E-9 = 0
⇒ X = 4.333 E-9 M
according Henderson-Hauselbach:
- pH = pk + Log [A-] / [HA]
∴ [OBr-] = 0.3 mol/ 1 L + 4.333 E-9 M = 0.300 M
∴ [HOBr] = 0.5 mol / 1 L - 4.33 E-9 M = 0.500 M
∴ pKa = - log Ka = - Log ( 2.0 E-9 ) = 8.6989
⇒ pH = 8.6989 + Log ( 0.300/0.500 )
⇒ pH = 8.477
Because there are many numbers of the human measurement . we must manage the uncertainly doing calculations because we can know what we are calculating.
The answer is B.
First write a balanced equation, which is
4Fe + 3O2 => 2Fe2O3.
Then divide the grams of Fe by the molar mass of Fe (16.7/55.85).
You now know the number of moles of Fe, so perform dimensional analysis.
(.299*2*159.70)/(4*1) = 23.9 g