feat(bokeh): implement titration-curve (#5177)

## Implementation: `titration-curve` - bokeh

Implements the **bokeh** version of `titration-curve`.

**File:** `plots/titration-curve/implementations/bokeh.py`

**Parent Issue:** #4407

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/23389866006)*

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: github-actions[bot]

plots/titration-curve/implementations/bokeh.py

@@ -0,0 +1,227 @@
+""" pyplots.ai
+titration-curve: Acid-Base Titration Curve
+Library: bokeh 3.9.0 | Python 3.14.3
+Quality: 91/100 | Created: 2026-03-21
+"""
+
+import numpy as np
+from bokeh.io import export_png, save
+from bokeh.models import BoxAnnotation, ColumnDataSource, HoverTool, Label, LinearAxis, Range1d, Span
+from bokeh.plotting import figure
+from bokeh.resources import CDN
+
+
+# Data - Strong acid/strong base titration: 25 mL of 0.1 M HCl with 0.1 M NaOH
+acid_volume_ml = 25.0
+acid_concentration = 0.1
+base_concentration = 0.1
+equivalence_volume = acid_volume_ml * acid_concentration / base_concentration  # 25 mL
+
+volume_ml = np.unique(
+    np.concatenate([np.linspace(0.1, 24.0, 80), np.linspace(24.0, 26.0, 40), np.linspace(26.0, 50.0, 80)])
+)
+
+moles_acid = acid_concentration * acid_volume_ml / 1000
+moles_base = base_concentration * volume_ml / 1000
+total_volume_L = (acid_volume_ml + volume_ml) / 1000
+
+ph = np.empty_like(volume_ml)
+for i in range(len(volume_ml)):
+    if moles_base[i] < moles_acid - 1e-10:
+        h_plus = (moles_acid - moles_base[i]) / total_volume_L[i]
+        ph[i] = -np.log10(h_plus)
+    elif moles_base[i] > moles_acid + 1e-10:
+        oh_minus = (moles_base[i] - moles_acid) / total_volume_L[i]
+        ph[i] = 14.0 + np.log10(oh_minus)
+    else:
+        ph[i] = 7.0
+
+# Derivative dpH/dV using central differences
+dph_dv = np.gradient(ph, volume_ml)
+dph_dv = np.where(np.isfinite(dph_dv), dph_dv, 0.0)
+eq_ph = 7.0
+
+# Colors
+CURVE_COLOR = "#306998"
+DERIV_COLOR = "#D55E00"
+EQ_COLOR = "#009E73"
+ACID_BUFFER_COLOR = "#E69F00"
+BASE_BUFFER_COLOR = "#56B4E9"
+BG_COLOR = "#F7F7F7"
+AXIS_COLOR = "#444444"
+
+source = ColumnDataSource(data={"volume": volume_ml, "ph": ph, "dph_dv": dph_dv})
+
+# Plot
+p = figure(
+    width=4800,
+    height=2700,
+    x_axis_label="Volume of NaOH added (mL)",
+    y_axis_label="pH",
+    y_range=Range1d(0, 14),
+    title="titration-curve · bokeh · pyplots.ai",
+    toolbar_location=None,
+)
+
+# Buffer region shading - regions where pH changes slowly (excess acid / excess base)
+# Acid-excess region: 0-15 mL (excess HCl dominates, pH slowly rises)
+acid_buffer = BoxAnnotation(left=0, right=15, fill_color=ACID_BUFFER_COLOR, fill_alpha=0.08, line_color=None)
+p.add_layout(acid_buffer)
+
+# Base-excess region: 35-50 mL (excess NaOH dominates, pH plateaus)
+basic_buffer = BoxAnnotation(left=35, right=50, fill_color=BASE_BUFFER_COLOR, fill_alpha=0.08, line_color=None)
+p.add_layout(basic_buffer)
+
+# Region labels - chemically accurate for strong acid/strong base system
+p.add_layout(
+    Label(
+        x=7.5,
+        y=4.5,
+        text="Excess HCl Region",
+        text_font_size="20pt",
+        text_color="#C68600",
+        text_alpha=0.85,
+        text_align="center",
+        text_font_style="italic",
+    )
+)
+p.add_layout(
+    Label(
+        x=42.5,
+        y=9.5,
+        text="Excess NaOH Region",
+        text_font_size="20pt",
+        text_color="#3A8BC2",
+        text_alpha=0.85,
+        text_align="center",
+        text_font_style="italic",
+    )
+)
+
+# Secondary y-axis for derivative
+deriv_max = float(np.max(dph_dv)) * 1.15
+p.extra_y_ranges = {"deriv": Range1d(start=-deriv_max * 0.05, end=deriv_max)}
+deriv_axis = LinearAxis(
+    y_range_name="deriv",
+    axis_label="dpH/dV (mL⁻¹)",
+    axis_label_text_font_size="22pt",
+    major_label_text_font_size="18pt",
+    axis_line_color=DERIV_COLOR,
+    axis_label_text_color=DERIV_COLOR,
+    major_label_text_color=DERIV_COLOR,
+    major_tick_line_color=None,
+    minor_tick_line_color=None,
+)
+p.add_layout(deriv_axis, "right")
+
+# Derivative curve
+deriv_source = ColumnDataSource(data={"volume": volume_ml, "dph_dv": dph_dv})
+p.line(
+    "volume",
+    "dph_dv",
+    source=deriv_source,
+    line_width=4,
+    color=DERIV_COLOR,
+    line_alpha=0.8,
+    line_dash="dotdash",
+    y_range_name="deriv",
+    legend_label="dpH/dV",
+)
+
+# Main titration curve
+p.line("volume", "ph", source=source, line_width=5, color=CURVE_COLOR, legend_label="pH")
+
+# Equivalence point vertical dashed line
+p.add_layout(
+    Span(
+        location=equivalence_volume,
+        dimension="height",
+        line_color=EQ_COLOR,
+        line_width=3,
+        line_dash="dashed",
+        line_alpha=0.8,
+    )
+)
+
+# Equivalence point marker
+p.scatter([equivalence_volume], [eq_ph], size=26, color=EQ_COLOR, marker="diamond", line_color="white", line_width=2)
+
+# Equivalence point annotation - offset to reduce congestion
+p.add_layout(
+    Label(
+        x=equivalence_volume,
+        y=eq_ph,
+        text=f"Equivalence Point\n{equivalence_volume:.0f} mL, pH {eq_ph:.1f}",
+        text_font_size="22pt",
+        text_font_style="bold",
+        text_color=EQ_COLOR,
+        x_offset=35,
+        y_offset=-30,
+    )
+)
+
+# pH 7 reference line
+p.add_layout(
+    Span(location=7, dimension="width", line_color="#999999", line_width=1.5, line_dash="dotted", line_alpha=0.35)
+)
+
+# Hover tool
+p.add_tools(
+    HoverTool(tooltips=[("Volume", "@volume{0.1} mL"), ("pH", "@ph{0.2}")], mode="vline", line_policy="nearest")
+)
+
+# Style
+p.title.text_font_size = "36pt"
+p.title.text_font_style = "normal"
+p.title.text_color = "#2B2B2B"
+p.title.offset = 10
+
+p.xaxis.axis_label_text_font_size = "26pt"
+p.yaxis.axis_label_text_font_size = "26pt"
+p.xaxis.major_label_text_font_size = "20pt"
+p.yaxis.major_label_text_font_size = "20pt"
+p.xaxis.axis_label_standoff = 18
+p.yaxis.axis_label_standoff = 18
+
+p.xaxis.axis_line_color = AXIS_COLOR
+p.yaxis.axis_line_color = AXIS_COLOR
+p.xaxis.axis_line_width = 1.5
+p.yaxis.axis_line_width = 1.5
+
+p.xaxis.major_tick_line_color = None
+p.yaxis.major_tick_line_color = None
+p.xaxis.minor_tick_line_color = None
+p.yaxis.minor_tick_line_color = None
+
+p.outline_line_color = None
+p.background_fill_color = BG_COLOR
+p.border_fill_color = "#FFFFFF"
+
+p.ygrid.grid_line_alpha = 0.18
+p.ygrid.grid_line_width = 1
+p.ygrid.grid_line_dash = [6, 4]
+p.xgrid.grid_line_alpha = 0.12
+p.xgrid.grid_line_width = 1
+p.xgrid.grid_line_dash = [6, 4]
+
+p.min_border_left = 120
+p.min_border_right = 180
+p.min_border_bottom = 80
+p.min_border_top = 60
+
+# Legend
+p.legend.location = "top_left"
+p.legend.label_text_font_size = "22pt"
+p.legend.glyph_height = 35
+p.legend.glyph_width = 50
+p.legend.spacing = 14
+p.legend.padding = 22
+p.legend.margin = 20
+p.legend.background_fill_alpha = 0.9
+p.legend.background_fill_color = "#FFFFFF"
+p.legend.border_line_color = "#CCCCCC"
+p.legend.border_line_width = 1.5
+
+# Save
+export_png(p, filename="plot.png")
+save(p, filename="plot.html", resources=CDN, title="titration-curve · bokeh · pyplots.ai")