Answers toStudent Questions

All IB Mathematics IB Sciences IB Individuals & Societies IB English IB Language B

Chemistry

Can chlorine have an expanded octet?

Yes, chlorine can have an expanded octet because it has empty $3d$ orbitals available that can accommodate more than eight electrons. As a Period 3 element, chlorine has access to $3s,$ $3p,$ and $3d$ orbitals, which allows it to form compounds where it is surrounded by more than eight electrons. Common examples include $\ce{ClF3}$ (chlorine trifluoride) where chlorine has 10 electrons around it, and $\ce{ClF5}$ (chlorine pentafluoride) where chlorine has 12 electrons. This ability to expand the octet is only possible for elements in Period 3 and beyond because they have $d$ orbitals available in their valence shell.

Psychology

What is standard deviation in psychology?

The standard deviation is a measure of dispersion that shows how spread out the values in a data set are around the mean. It indicates the extent to which individual data points differ from the average. A smaller standard deviation means the data are closely clustered around the mean, while a larger one suggests greater variability. Because it is based on the original data, the standard deviation uses the same unit of measurement. For example, in a psychology study recording participants' reaction times in seconds, the standard deviation would also be in seconds. A low standard deviation would indicate that most participants responded at similar speeds, whereas a high standard deviation would reflect more varied reaction times.

Biology

What does starch do for a plant?

Starch plays a vital role in plants by serving as a storage form of glucose. During photosynthesis, plants often produce more glucose than they immediately require. To manage this surplus, they convert the excess glucose into starch—a carbohydrate that can be hydrolysed and respired to release energy when needed. This stored energy supports essential processes such as growth, repair, and survival, particularly when photosynthesis slows or stops, such as at night or during winter. Biochemically, starch is composed of two types of polysaccharides: amylose and amylopectin. Amylose consists of alpha-glucose units joined by α 1-4 glycosidic bonds, forming a linear, coiled structure. Amylopectin, by contrast, is branched and contains both α 1-4 and α 1-6 glycosidic linkages between the alpha-glucose molecules. The α-1,6 glycosidic linkages cause branching, which allows amylopectin to be broken down more rapidly than amylose. This structural difference makes amylopectin particularly useful when the plant needs to quickly access stored glucose. Starch is typically stored in organs such as roots, seeds, tubers, and some leaves. When environmental conditions limit photosynthesis, the plant hydrolyses starch back into glucose. This glucose is then used in cellular respiration to generate ATP, providing energy for vital metabolic activities. Because starch is insoluble, it does not affect the osmotic potential of the cell where it is stored, allowing glucose to be stored without disrupting water balance. This property allows plants to store large quantities of glucose without disrupting cellular function or water potential. In summary, starch enables plants to maintain a stable and accessible energy reserve. Its biochemical structure, efficient storage capacity, and osmotic neutrality make it ideal for managing energy needs when photosynthetic activity is reduced. This function is fundamental to plant survival, development, and adaptation to changing environmental conditions.

Physics

Why is specific heat important?

Specific heat is defined as the amount of thermal energy required to raise the temperature of a unit mass of a substance by one degree of temperature. It is important because it determines the amount of energy that needs to be added or removed to heat up or cool down a substance or an object. The IB Physics data booklet formula involving specific heat is $\hspace{2em}$ $Q = mc\Delta T$ Where $\hspace{2em}$ $Q$ is the heat required in J\ $\hspace{2em}$ $m$ is the mass of the sample in kg\ $\hspace{2em}$ $c$ is the specific heat capacity of the substance \ $\hspace{2em}$ $\Delta T$ is the change in temperature in k. This formula can be rearranged to solve for specific heat capacity to get $\hspace{2em}$ $c = \dfrac{Q}{m\Delta T}$ We can see from the formula that the units on $c$ will be J kg$^{-1}\ ^o$C$^{-1}$. Substances with high values of specific heat require more energy for a given change in temperature than substances with a lower value for specific heat. Water is an example of a substance with a high specific heat, with $c$ equal to 4186 J kg$^{-1}\ ^o$C$^{-1}$. This relatively high value means that a significant amount of energy is required to raise water to its boiling point. It also means that a lot of energy is released when water cools down again. Some older heating systems in houses circulate hot water to deliver heat to the rooms. Water’s high carrying capacity for thermal energy makes it ideal for this use. Another example of where water’s high specific heat plays an important role is in weather. Although the land may heat up and cool down relatively quickly as the air temperature changes, bodies of water will take much more time for their temperature to change. In summer, the water will stay cooler than the air and help moderate extreme heat. Similarly, in winter bodies of water can help moderate very cold air temperatures. Because of our understanding of specific heat, we can calculate the heat capacity of objects. This is the amount of energy required to raise an object's temperature by one degree kelvin. Once this is known, we can predict the rate at which objects will change temperature and the amount of heat energy involved. Understanding specific heat is extremely valuable for designing systems where heat transfer is fundamental to their operation.

Mathematics

What is the tangent graph?

The tangent graph is the graph of a trigonometric function. $\tan x$ is a trigonometric ratio. If we substitute $x$ values into the function $y=\tan x$ then we generate a $\textbf{tangent graph}$. Like many graphs, the tangent graph has distinct characteristics. First we note that the trigonometric ratios, including tangent, have periodicity (i.e. they repeat a pattern over a certain period). For the standard tangent graph, the period is $\pi$ which means every $\pi$ units along the $x$-axis the pattern repeats itself. Another characteristic of the tangent graph is that there are vertical asymptotes. Tangent is the ratio of the sine function to the cosine function $$ \begin{align*} \tan x=\frac{\sin x}{\cos x} \end{align*} $$ so whenever the cosine function equals zero $(\cos x=0)$ then the tangent curve has a vertical asymptote, because we are not able to divide by $0$. Due to this, we cannot substitute every $x$ value. The domain of tangent is $\{x\in\mathbb{R}, x\neq\frac{\pi}{2},\frac{3\pi}{2}, \frac{5\pi}{2}...\}$. Between the asymptotes, the tangent graph starts from negative infinity, passes through the $x$-axis halfway between the asymptotes, and then rapidly increases to positive infinity as it approaches the next asymptote. Hence the range of values of tangent is $\{y\in\mathbb{R}\}$. It is not a straight diagonal line but increases rapidly near the asymptotes and has a more shallow gradient as it passes through the $x$-axis.

Explore More IB Math Resources

Over 80% of IB students globally are experiencing the power of Revision Village

Questionbank

Practice Exams

Key Concepts